UC-NRLF 


S3b 


MANUAL 

OF 

WIRELESS  TELEGRAPHY 

FOR  THE  USF,  OF 

NAVAL  ELECTRICIANS 
1911 


r 


MANUAL 


OF 


WIRELESS  TELEGRAPHY 


FOR  THE  USE  OF 


NAVAL  ELECTRICIANS 


1 


MANUAL 


OF 


WIRELESS  TELEGRAPHY 


FOR  THE  USE  OF 


NAVAL  ELECTRICIANS 


BY 

COMMANDER  S.  S.  ROBISON,  U.  S,  NAVY 


2D  REVISED  EDITION 


ANNAPOLIS,   MD. 

THE  UNITED  STATES  NAVAL  INSTITUTE 
1911 


CONTENTS 


CHAPTER  I. 
GENERAL  REVIEW  OF  FACTS  RELATING  TO  HIGH-FREQUENCY  CURRENTS. 

Electricity;  Magnetism;  Electro-magnetism;  Electro-magnetic  induction; 
Methods  of  producing  currents  by  electro-magnetic  induction;  Method  of  pro- 
ducing currents  used  in  wireless  telegraphy;  Electric  and  magnetic  fields; 
Electric  capacity;  Electric  induction;  Electric  condensers;  Discharge  of  con- 
densers; Ether  waves;  Reflection;  Refraction;  Diffraction;  and  Production  of 
ether  waves. 

CHAPTER  II. 

UNITS. 

Foot-pound-minute;  Centimeter-gram-second;  Power;  Work;  Dyne;  Erg; 
Volt;  Ampere;  Ohm;  Watt;  Coulomb;  Farad;  Henry. 

CHAPTER  III. 
CAPACITY,  SELF-INDUCTION,  AND  MUTUAL  INDUCTION. 

Fundamental  equation  of  wireless  telegraphy;  Difference  between  D.  C. 
and  A.  C.  due  to  self-induction  and  capacity;  Skin  effect  of  high  frequency 
currents;  Self-induction  and  capacity  of  straight  wires;  Mutual  induction. 

CHAPTER  IV. 
ELECTRIC  OSCILLATIONS. 

Radiation  of  electric  waves;  Damped  and  undamped  oscillations;  Wave 
trains;  Work  done  in  producing  electric  waves  and  making  dots  and  dashes 
of  the  telegraph  code;  Detection  of  electric  waves. 

CHAPTER  V. 
SENDING  CIRCUITS  AND  APPARATUS. 

Generators;  Transformers;  Regulation  of  sending  sets;  Sending  keys; 
Closed  circuit  inductances;  Condensers  and  condenser  material;  Spark  gaps; 
Energy  transfer  between  closed  and  open  circuits;  Limitations  on  wave 
lengths;  Aerials  (Antenna);  Anchor  spark  gap;  Lightning  switch;  Open- 
circuit  inductances;  Variometers;  Hot-wire  ammeter;  Grounds  and  ground 
connections. 

CHAPTER  VI. 

RECEIVING  CIRCUITS  AND  APPARATUS. 

Open  circuit;  Closed  circuit;  Inductances;  Condensers;  Detectors;  Tele- 
phones; Batteries;  Buzzers;  Ampliphones;  Recorders. 


8  CONTENTS. 

• 

CHAPTER  VII. 
INSTALLATION  AND  OPERATION. 

Installation;    Adjustments;    Calibration;    Tuning;    Wave  meters  and  their 
use;  Measurements;  Care  and  operation;  Codes. 

CHAPTER  VIII. 
MISCELLANEOUS. 

Wireless  telephony;    Production  of  undamped  oscillations;   Directive  wire- 
less telegraphy;  Portable  wireless  sets;  Static;  Standard  wave  lengths. 

APPENDICES. 
INDEX. 


MANUAL  OF  WIRELESS  TELEGRAPHY. 


Chapter  I. 

GENERAL  REVIEW  OF  FACTS  RELATING  TO  HIGH 
FREQUENCY  CURRENTS. 

ELECTRICITY. 

1.  If  amber  is  rubbed  with  silk  a  change  in  the  condition  of  the  amber 
and  of  the  silk  is  produced  which  can  be  detected  in  various  ways. 

This  change  in  condition  is  described  by  saying  that  the  amber  and 
the  silk  are  electrified  or  charged  with  electricity  by  friction.  Both  of 
these  terms  are  derived  from  the  Greek  word  "  elektron,"  meaning  amber. 

The  silk  and  amber  thus  electrified  attract  each  other  and  bodies  in 
their  -vicinity,  but  the  silk  will  repel  another  piece  of  silk  similarly 
electrified  and  the  amber  will  repel  another  piece  of  amber  similarly 
electrified.  Since  amber  and  silk  have  no  effect  on  each  other  when  not 
electrified,  the  qualities  of  attraction  and  repulsion  are  said  to  reside  in 
the  electric  charges,  and  the  fact  is  expressed  by  the  statement  that  like 
charges  repel,  unlike  charges  attract  each  other.  The  silk  is  said  to  be 
positively,  the  amber  negatively,  electrified  or  charged.  Positive  and 
negative  charges  are  indicated  by  plus  (  + )  and  minus  ( — )  signs. 

The  charges  are  said  to  consist  of  static  or  frictional  electricity. 

Bodies  thus  charged  when  not  brought  into  contact  with  each  other 
or  with  what  are  called  conductors  remain  in  an  electrified  condition  for 
some  time. 

Bringing  oppositely  charged  bodies  in  contact  generally  removes  all 
evidences  of  electrification.  The  charges  are  said  to  unite  and,  being  of 
opposite  signs,  to  neutralize  each  other,  and  the  bodies  are  said  to  be 
discharged. 

Sparks  accompanied  by  a  sharp  crackling  sound  are  produced  between 
highly  electrified  bodies  when  brought  very  near  each  other.  After  the 
spark  has  passed  the  bodies  are  found  to  be  discharged. 

Charged  bodies  which  can  be  discharged  by  sparking  at  greater  dis- 
tances than  others  are  said  to  be  charged  to  a  higher  potential- 
All  bodies,  whatever  their  nature,  are  capable  of  being  electrified. 

The  presence  of  static  charges  of  electricity  can  be  shown  by  what 
are  called  electroscopes.  One  of  the  most  sensitive,  the  gold-leaf  electro- 
scope, consists  of  two  small  pieces  of  gold  leaf,  which,  becoming  charged 


10 


MANUAL    OF    WIRELESS    TELEGRAPHY. 


in  the  same  sense  (i.  e.,  positively  or  negatively),  by  touching  a  charged 
body,  repel  each  other,  and  diverge,  and  show  by  their  divergence  the 
presence  of  electric  charges. 

2.  Certain  bodies,  notably  metals,  have  the  quality  of  transmitting  or 
carrying  electric  charges  through  themselves  and  are  called  conductors. 
Bodies  lacking  in  this  quality,  or  possessing  it  to  a  very  limited  degree, 
are  called  nonconductors,  or  insulators,  or  dielectrics,  according  to  the 
purpose  for  which  they  are  used. 

3.  When  pieces   of  zinc  and  carbon   are  immersed  in  a   conducting 
liquid   (fig.  l).the  combination  is  called  a  primary  cell.     If  a  wire  is 
connected  to  the  zinc  and  one  to  the  carbon  and  the  free  ends  of  the 
two  wires  brought  near  each  other,  these  ends  are  found  to  be  electrified ; 
the  end  of  the  wire  connected  to  the  carbon  electrified  like  the  silk  ( + ) 
and  the  end  of  that  connected  to  the  zinc  like  the  amber  ( — ) .     The 
carbon  is  called  the  negative  element  or  positive  pole  of  the  cell  and  the 


FIG.  1. 


FIG.  2. 


zinc  the  positive  element  or  negative  pole.  A  number  of  cells  together  is 
called  a  battery.  The  liquid  in  which  the  elements  are  immersed  is  called 
the  battery  solution.  If  the  free  ends  of  the  wires  are  brought  together 
an  electric  current  is  established,  of  which  the  positive  direction  is"  said 
to  be  from  the  carbon  to  the  zinc,  through  the  wires;. from  the  zinc  to  the 
carbon,  through  the  liquid.  (See  fig.  2,  and  note  1,  appendix.) 

The  current  is  said  to  be  caused  by  a  difference  of  potential  between 
the  carbon  and  the  zinc.  It  is  supposed  to  be  made  up  of  small  electric 
charges  transmitted  through  the  wire  in  quick  succession,  the  charges 
being  produced  by  chemical  or  electric  action  between  the  carbon  and 
the  zinc  in  the  liquid. 

The  force  which  causes  the  movement  of  the  electric  charges  which 
make  up  the  current  is  called  the  electro-motive  force  and  is  usually 
written  E.  M.  F. 

If  the  free  ends  of  the  wire  in  fig.  2  instead  of  being  directly  con- 
nected are  immersed  in  another  conducting  liquid,  as  in  fig.  3,  the  cur- 
rent will  flow  through  this  liquid.  The  immersed  ends  are  called 
electrodes.  The  one  at  which  the  current  enters  is  called  the  positive 
and  the  one  at  which  it  emerges  the  negative  electrode.  These  are  also 


MANUAL   OF   WIRELESS   TELEGRAPHY. 


11 


called  the  anode  and  the  cathode,  respectively.     The  conducting  liquid 
in  this  cell  is  called  the  electrolyte. 

4.  If  the  anode  and  cathode  in  fig.  3  are  made  of  lead  (or  prepara- 
tions of  lead)  plates,  and  the  electrolyte  is  a  solution  of  sulphuric  acid 
in  water,  the  combination  is  called  a  secondary  or  storage  cell  or  accumu- 
lator and  a  number  of  such  cells  is  called  a  storage  lattery.  The 


FIG.  4. 


anode  is  called  the  positive  plate  and  the  cathode  the  negative  plate.  If, 
after  a  current  has  been  forced  through  such  a  cell  for  a  time,  the  wires 
from  the  primary  cells  are  disconnected  and  the  positive  and  negative 
plates  connected  by  a  wire  (fig.  4)  outside  of  the  electrolyte,  a  current 
will  flow,  the  positive  direction  of  which  will  be  from  the  positive  to 
the  negative  plate  in  the  wire,  and  from  the  negative  to  the  positive 
plate  in  the  electrolyte. 

5.  For  convenience,  a  battery  of  primary  or  secondary  (storage)  cells 
is  indicated  as  in  fig.  5,  the  elements  forming  positive  poles  by  the  light 


FIG.  5. — Cells  in  Series. 


FIG.  SA. — Cells  in  Parallel. 


lines  and  the  elements  forming  negative  poles  by  the  shorter,  heavy  lines. 
Cells  connected  as  in  fig.  5  are  said  to  be  in  series;  connected  as  in  fig. 
5a,  in  parallel. 

MAGNETISM. 

6.  A  magnet  situated  at  a  distance  from  other  magnets  and  pivoted 
so  that  it  is  free  to  move,  will  point  toward  the  north  magnetic  pole  of 
the  earth,  which  in   some  localities   coincides  with  the  north  star  in 
2 


MANUAL    OF    WIRELESS    TELEGRAPHY. 


direction.  That  end  of  the  magnet  which  points  in  the  direction  of  the 
north  star  is  called  the  north-seeking  pole,  or  simply  the  north  pole  of  the 
magnet.  The  other  end  is  called  the  south  pole. 

Similar  magnetic  poles,  like  similarly  charged  bodies,  repel  each  other. 
Dissimilar  magnetic  poles,  like  oppositely  charged  bodies,  attract  each 
other — i.  e.,  two  north  poles  or  two  south  poles  repel  each  other :  a  north 
and  a  south  pole  attract  each  other.  The  north  pole  is  sometimes  called 
the  positive  pole  and  the  south  pole  the  negative  pole  of  the  magnet. 

Wrought  or  soft  iron  can  be  magnetized  but  only  retains  its  magnet- 
ism while  under  the  influence  of  the  magnetizing  force;  steel  or  hard 
iron  once  magnetized  retains  its  magnetization  permanently,  and  special 
means  to  demagnetize  it  are  required. 

All  bodies  can  be  electrified,  but  all  bodies  can  not  be  magnetized. 

7.  If  a  sheet  of  paper  is  held  over  a  powerful  magnet  and  iron  filings 
sprinkled  on  the  sheet,  the  filings  will  assume  positions  approximately 


FIG.  6. 


FIG.  7. 


as  shown  in  fig.  6.  Some  force  connected  with  the  magnet  must  make 
the  filings  assume  these  positions,  which  are  different  from  what  they 
would  be  if  the  magnet  was  not  under  the  paper;  and  from  the  way  the 
filings  are  arranged,  this  force  must  act  in  'the  space  surrounding  the 
magnet.  This  space  is  called  the  field  of  magnetic  force,  or  simply  the 
field  of  force,  and  the  lines  in  which  the  filings  tend  to  arrange  them- 
selves are  called  the  lines  of  force,  and  we  shall  see  in  chapter  II  that  this 
conception^  used  as  a  basis  for  electric  measurements.  The  direction  of 
the  lines  of  force  at  any  point  indicates  the  direction  of  the  magnetic 
force  at  that  point,  and  their  number  in  any  area,  the  strength  of  the 
field  in  that  area. 

It  is  found  that  a  small  magnetic  needle,  pivoted  so  that  it  is  free  to 
move  and  brought  near  the  large  magnet,  will  lie  parallel  to  the- direction 
of  the  lines  of  force  at  any  point  at  which  it  may  be  placed  in  the  field, 


MANUAL    OF   WIRELESS    TELEGRAPHY.  13 

and  that  the  north  pole  of  the  needle  always  points  along  the  lines  of 
force  in  the  direction  leading  to  the  south  pole  of  the  magnet. 

The  direction  in  which  the  north  pole  of  the  needle  points  is  called 
the  positive  direction  of  the  lines  of  magnetic  force,  and  the  direction 
in  which  the  south  pole  points,  the  negative  direction  of  the  lines  of 
magnetic  force. 

Lines  of  magnetic  force  are  said  to  run  from  the  north  pole  of  the 
magnet  to  the  south  pole  through  the  air,  and  back  to  the  north  pole 
through  the  steel  (fig.  7). 

ELECTRO-MAGNETISM. 

8.  If  the  wire  in  fig.  1  is  coiled  into  a  spiral,  as  in  fig.  8,  with  the 
positive  direction  of  the  electric  current  as  shown  by  the  arrows  and 


FIG.  8. 

the  battery  connections,  a  field  of  magnetic  force  which  can  be  explored 
by  a  small .  magnetic  needle,  or  outlined  by  iron  filings,  as  in  fig.  6, 
will  be  found  to  exist  around  the  spiral,  and  the  direction  of  the  lines  of 
force  will  be  found  the  same  as  those  around  the  magnet  in  fig.  7.  If  the 
current  is  reversed,  the  lines  of  force  are  reversed  in  direction. 

Such  a  spiral,  when  traversed  by  a  current,  is  found  to  have  all  the 
properties  of  a  magnet,  and  is  called  an  electro-magnet  or  solenoid. 

The  strength  of  the  magnetic  field  around  an  electro-magnet  rises 
and  falls  with  the  rise  and  fall  of  the  current,  and  its  polarity  depends 
on  the  direction  of  the  current. 

The  positive  direction  of  the  lines  of  magnetic  force  which  surround 
a  solenoid  is  from  the  north  to  the  south  pole  outside  of  the  spiral,  and 
from  the  south  to  the  north  pole  inside  of  it,  just  as  the  positive  direction 


14  MANUAL   OF    WIRELESS    TELEGRAPHY. 

of  an  electric  current  is  from  the  positive  pole  to  the  negative  pole  out- 
side of  a  battery  and  from  the  negative  to  the  positive  pole  inside  of  it. 
If  the  number  of  turns  of  the  spiral  is  reduced  to  one  it  does  not 
lose  its  magnetic  character.  The  lines  of  force  then  form  circles  around 
the  wire,  their  positive  direction  being  shown  in  fig.  9,  the  upper  side 
being  a  north  pole  and  the  under  side  a  south  pole.  If  the  turn  is 
straightened  out,  as  in  fig,  10,  the  lines  of  force  still  form  circles  around 
the  wire,  and  the  north  pole  of  the  exploring  needle  points  in  the  positive 
direction  of  those  lines.  This  direction  is  found  to  be  always  at  right 
angles  to  the  wire. 


FIG.  9.  •  FIG.  10. 


9.  It   appears   from   the  foregoing  that  what  is   called  the  positive 
direction  of  motion  of  electric  currents,  or  charges,  is  related  to  what 
is  called  the  positive  direction  of  the  lines  of  magnetic  force,  in  the 
manner  shown  by  the  arrows  in  figs.  8,  9,  and  10,  and,  further,  that 
the  terms  positive  and  negative  as  applied  to  electric  and  magnetic  effects, 
and  so  largely  used  in  connection  with  them,  are  purely  conventional. 
(See  note  2,  appendix.) 

10.  Returning  now  to  the  statement  in  article  8  that  the  strength 
of  the  magnetic  field  around  a  solenoid  rises  and  falls  -with  the  strength 
of  the  current,  and  its  polarity  (i.  e.,  the  direction  of  the  lines  of  mag- 
netic force  produced)  depends  on  the  direction  of  the  current,  it  can  be 
further  stated  that  a  magnetic  field  exists  around  every  wire  carrying 
an  electric  current  (fig.  10).    The  direction  of  the  lines  of  force  in  this 
field  depends  on  the  direction  of  the  current.    These  lines  of  force  always 
enclose  circles  in  planes  at  right  angles  to  the  wire. 

11.  Since  a  current  is  conceived  to  be  made  up  of  a  quick  succession 
of  moving  electric  charges   (art.  3),  the  above  facts  may  be  stated  in 
another  way,  viz.,  that  moving  electric  charges  produce  magnetic  fields 
in  which  the  lines  of  magnetic  force  enclose  circles  in  planes  at  right 
angles  to  the  direction  of  motion  of  the  moving  charges.    This  has  been 
proved  to  be  true  for  single  static  charges.* 

ELECTRO-MAGNETIC  INDUCTION. 

12.  Fig.  11  represents  a  primary  battery,  with  the  two  poles  of  the 
battery  connected  by  a  conducting  wire,  broken  at  K.    A  straight  portion 

*  By  Professor  Rowland,  Johns  Hopkins  University. 


MANUAL    OF    WIRELESS    TELEGRAPHY. 


15 


FIG.  11. 


A  B  of  this  wire  is  parallel  to,  and  at  a  distance  from  another  conducting 
wire  C  D.  When  the  break  at  K  is  closed,  a  current  flows  in  the  circuit, 
and  a  field  of  force  is  created  around  the  wire.  Let  us  consider  the 
straight  portion  A  B  in  which  the  direction  of  the  current  is  shown  by 
the  arrows,  and  the  direction  of  the  lines  of  force  by  the  circles  (shown 
as  ellipses),  at  right  angles  to  A  B.  Several  of  these  lines  of  force  are 
shown  embracing  the  parallel  wire  C  D. 

If  gold-leaf  electroscopes  (art.  1)  are  attached 
to  the  ends  C  and  D  of  the  wire  C  D,  and  if  the 
current  started  in  A  B  when  the  break  is  closed 
is  sufficiently  powerful,  the  gold  leaves  will  be 
observed  to  diverge,  momentarily,  whenever  the 
circuit  is  made  or  broken  at  K.  The  stronger  the 
current  in  A  B,  and  consequently  the  stronger 
the  magnetic  field  produced,  the  more  pronounced 
the  indications  of  the  electroscope  will  be. 

This  shows  that  the  ends  C  and  D  of  the  wire 
C  D  are  electrified  when  the  current  is  made  or 
broken  in  A  B.  When  the  current  is  made,  the 

end  D  is  negatively  charged  like  the  amber  and  like  the  wire  attached  to 
the  zinc  element  in  fig.  1,  the  end  C  positively,  like  the  silk  and  like  the 
wire  attached  to  the  carbon  element  in  fig.  1. 

When  the  circuit  is  broken  at  K  the  electrification  of  C  D  is  reversed, 
C  becoming  negatively  and  D  positively  electrified.  A  sudden  increase 
or  decrease  of  the  current  in  A  B  produces  the  same  effect  as  when  the 
current  is  made  or  broken. 

It  is  to  be  noted  that  the  electrification  of  C  D  is  only  momentary. 
As  soon  as  the  causes  producing  it  are  removed,  the  electric  charges 
unite  and  neutralize  each  other  through  the  body  of  the  conductor. 

We  know  that  when  the  current  in  A  B  is  made,  a  magnetic  field  is 
created  around  A  B  which  extends  to  and  beyond  C  D,  and  that  when  the 
current  in  A  B  is  broken,  the  magnetic  field  disappears,  and  that  the 
only  thing  common  to  A  B  and  C  D  is  this  magnetic  field,  the  lines  of 
force  in  which  surround  them  both,  and  since  we  see  that  one  kind  of 
electrification  is  produced  in  C  D  when  the  lines  of  force  are  being 
created,  and  the  opposite  kind  when  they  are  being  dissipated,  we  con- 
clude that  the  movement  or  creation  of  these  lines  creates  the  electric 
charges  that  we  observe  in  C  D. 

13.  In  art.  11  it  is  stated  that  moving  electric  charges  create  magnetic 
lines  of  force.  Now,  we  see  the  truth  of  the  converse,  viz.,  that  moving 
magnetic  lines  of  force  create  electric  charges. 

These  two  facts  are  of  general  application  and  are  the  basis  of  all 
electro-magnetic  calculations. 


16 


MANUAL    OF    WIRELESS    TELEGRAPHY. 


14.  It  is  of  great  importance  to  keep  clearly  in  mind  the  fact  that 
electrification  in  C  D  only  takes  place  when  the  current  is  made  or 
broken  or  changed  in  A  B.    When  there  is  no  current  in  A  B  there  are 
no  magnetic  lines  of  force,  and  consequently  there  is  no  electrification 
in  C  D.    When  there  is  a  constant  current  in  A  B  the  magnetic  field  is 
constant  and  there  is  no  electrification  in  C  D. 

It  is  while  the  current  in  A  B  is  rising  or  falling,  and-  the  lines  of 
force  expanding  from  or  contracting  toward  A  B  and  cutting  through 
C  D  as  they  pass,  that  C  D  is  affected.  A  movement  of  the  lines  of  force 
is  required  to  electrify  C  D,  and  this  movement  is  produced  by  changes 
in  the  current  in  A  B. 

If  the  ends  C  and  D  are  joined  to  form  a  complete  circuit,  a  momen- 
tary current  will  flow  when  changes  in  the  magnetic  field  around  C  D 
take  place. 

We  have  just  seen  that  a  moving  magnetic  field  in  the  vicinity  of  C  D 
creates  electric  charges  in  C  D.  We  would  also  find  that  moving  C  D 
in  a  magnetic  field  has  the  same  effect.  The  change  of  current  in  A  B 
is  said  to  induce  the  current  in  C  D,  and  the  action  is  called  electro- 
magnetic induction. 

The  preceding  facts  can  be  stated  as  follows :  When  magnetic  lines 
of  force  cut  or  are  cut  by  a  conductor,  electric  charges  (i.  e.,  a  tendency 
to  current  flow)  are  induced  in  the  conductor,  and  currents  flow  if  the 
conductor  forms  a  closed  circuit,  the  direction  of  the  induced  currents 
depending  on  the  direction  of  cutting. 

15.  When  the  current  in  A  B  is  rising,  the  magnetic  lines  of  force 
are  expanding,  and  cutting  C  D  in  the  direction  from  left  to  right,  the 
direction  of  the  momentary  current  in  C  D  being  as  shown  in  fig.  lla. 


FIG.  HA. — Current  in  A-B  Rising. 


B          P 

FIG.  HB. — Current  in  A-B  Falling. 


When  the  current  in  A  B  is  falling,  the  magnetic  lines  of  force  are 
contracting,  and  cutting  C  D  in  the  direction  from  right  to  left,  the 
direction  of  momentary  current  in  C  D  being  shown  in  fig.  lib.  These 
momentary  currents  or  movements  of  electric  charges  in  C  D  themselves 


MANUAL    OF    WIRELESS    TELEGRAPHY. 


17 


produce  momentary  magnetic  fields  around  C  D,  the  direction  of  the 
lines  of  force  of  which  are  shown  by  the  arrows  in  figs,  lla  and  lib. 
It  will  be  seen  that  these  lines  of  force  are  opposite  in  direction  to  those 
which  created  the  current  in  C  D.  ,The  field  of  force  created  around 
C  D  reacts  upon  A  B,  tending  to  create  in  A  B  a  current  in  the  opposite 
direction  to  that  already  in  A  B,  i.  e.,  to  stop  it. 

In  other  words,  the  change  of  primary  current  in  A  B  induces  a 
secondary  current  in  C  D.  The  latter  current  in  turn  induces  a  tertiary 
current,  which  is  in  A  B.  This  influence  of  two  currents  on  each  other 
is  called  their  mutual  induction. 

16.  The  electric  charges  produced  by  friction   (art.  1),  by  chemical 
action  (art,  3),  and  by  the  movement  of  lines  of  magnetic  force  are  all 
identical  in  their  properties,  and  the  magnetic  fields  produced  by  the 
movement  of  these  charges  are  also  identical  in  their  properties.     It  is 
therefore  evident  that  a  very  close  relation  exists  between  electricity  and 
magnetism. 

17.  We  have   seen  that  the  field  of  magnetic   force  around  a  wire 
carrying  a  current  or  around  a  magnet  can  be  mapped  out  by  iron 
filings.     In  a  similar  manner  the  field  of  electric  force  around  charged 
bodies  can  be  shown  by  the  use  of  various  light  powders. 

Figs.  12  and  12b  show  the  electric  field  between  unlike  and  like 
charges,  respectively.  Figs.  12a  and  12c  show  the  magnetic  field  between 


li2teSll/'^ 


FIG.  12. 


FIG.  12A. 


FIG.  12B. 


FIG.  12c. 


FIG.  12. — Electric  Field  Charges   of  Opposite  Sign. — Attraction. 
FIG.  12A. — Magnetic  Field  between  Unlike  Poles. — Attraction. 
FIG.  12B. — Electric  Field  Charges  of  Same  Sign. — Repulsion. 
FIG.  12c. — Magnetic  Field  between  Like  Poles. — Repulsion. 


18  MANUAL   OF   WIRELESS   TELEGRAPHY. 

unlike  and  like  poles,  respectively.  The  electric  field  between  two 
charged  bodies  is  found  to  resemble  very  closely  the  magnetic  field  be- 
tween magnet  poles.  In  all  figures  it  can  be  seen  that  in  electric  as  well 
as  magnetic  fields  each  line  of  force  appears  to  repel  its  neighbor,  and 
that  they  have  their  ends  on  points  of  opposite  electrification  or  magnet- 
ization. If  these  lines  tend  to  shorten  in  the  direction  of  their  length 
this  tendency  will  cause  the  attraction  between  the  bodies  from  which 
they  proceed. 

18.  It  may  be  asked, — what  are  these  lines  of  force  which  are  not 
visible  and  which  can  not  be  physically  grasped?    The  only  reply  is 
that  we  believe  all  electric  and  magnetic  phenomena  to  be  the  results  of 
the   disintegration   of   the   atoms   of  matter  or  the   rearrangement  of 
their  constituent  parts  (see  note  2,  appendix),  the  movements  of  which 
produce  stresses  and  consequent  movement  or  strains  in  what  is  called 
the  ether,  an  almost  infinitely  elastic,  infinitely  tenuous  substance  which 
surrounds  and  permeates  all  matter  and  all  space. 

The  earth  is  immersed  in  an  illimitable  ocean  of  ether,  just  as  fishes 
are  in  water. 

We  move  about  in  a  sea  of  it. 

What  we  call  electric  and  magnetic  fields  are  places  where  ether  move- 
ments and  ether  stresses  can  be  detected  by  the  phenomena,  which  they 
produce,  and  which  are  being  described. 

An  electric  field  is  a  state  of  strain  (stretch  or  compression)  in  the 
ether;  it  can  be  removed  between  any  two  points  by  connecting  them 
with  a  conductor.  The  release  of  the  strain  starts  movements  of  electric 
charges  in  the  conductor.  Movements  of  these  charges  produce  another 
state  of  strain  in  the  ether  at  right  angles  to  the  first.  We  call  this  a 
magnetic  field. 

We  have  seen  that  movement  of  either  field  creates  the  other,  and  that 
the  lines  of  force  in  the  two  fields,  when  they  are  thus  produced,  are  in 
planes  at  right  angles  to  each  other.  When  equilibrium  is  restored  one 
field  or  the  other  has  disappeared,  though  they  can  coexist  in  a  transitory 
state. 

19.  It  lias  been  proved  that  light  and  heat  are  forms  of  ether  motion 
also,  and  that  all  movements  (electric  and  magnetic)   in  the  ether  are 
propagated  with  the  velocity  of  light. 

It  has  also  been  proved  that  electric  movements  pi'ogress  along  straight 
wires  at  practically  the  same  speed  that  magnetic  movements  progress  at 
right  angles  to  them — i.  e.,  with  the  speed  of  light. 

This  velocity  has  been  measured  many  times  and  found  to  be  186,000 
miles,  or  approximately  300,000,000  meters  per  second. 

We  must  learn  therefore  to  think  of  light  movements  and  of  electric 


MANUAL    OF    WIRELESS    TELEGRAPHY.  19 

and  magnetic  actions  not  as  being  instantaneous,  but  as  being  restricted 
to  a  definite  measurable  speed. 

It  takes  time  for  electric  and  magnetic  effects  to  be  propagated  in  the 
ether,  time  for  them  to  be  propagated  along  a  wire.  The  wire  guides  or 
strikes  out  the  line  of  maximum  disturbance. 

20.  Let  us  now  return  to  fig.  11.  Before  connection  at  K  is  made, 
the  field  of  magnetic  force  does  not  exist,  but  the  wires  are  electrified 
by  means  of  action  between  the  zinc  and  carbon  in  the  battery  solution. 
When  the  break  at  K  is  closed,  a  magnetic  field  is  established;  when  the 
connection  at  K  is  broken,  the  magnetic  field  disappears.  The  question 
arises, — how  is  this  magnetic  field  created?  How  is  it  dissipated?  The 
reply  is:  It  is  created  by  movement  of  electric  charges  in  A  B  which 
disturb  the  ether  and  this  disturbance  is  propagated  through  the  ether 
at  right  angles  to  A  B,  with  the  speed  of  light,  i.  e.,  at  the  rate  of  186- 
000  miles  or  300,000,000  meters  per  second.  This  disturbance  is  of  such 
a  nature  as  to  produce  a  state  of  strain  in  the  ether  which  may  be 
compared  to  that  produced  in  a  piece  of  rubber  by  compression  or 
tension.  The  strain  is  relaxed  as  soon  as  its  cause  (i.  e.,  the  movement 
of  the  electric  charges)  is  removed. 

The  amount  of  strain  (i.  e.,  the  strength  of  the  magnetic  field) 
decreases  as  the  distance  from  the  moving  charges  increases.  It  spreads 
in  all  directions,  but  except  with  very  delicate  instruments  can  not  be 
detected  at  any  great  distance  from  A  B. 

The  creation  and  dissipation  of  this  state  of  unstable  equilibrium 
in  the  ether,  which  must  be  brought  about  by  some  kind  of  movement 
in  it,  produces  electrical  movement  in  C  D,  or,  as  it  is  perhaps  better 
to  say,  produces  electric  charges  in  CD.  CD  stands  in  the  way  of  and 
is  disturbed  by  an  advancing  or  receding  wave  of  movement  in  the  ether, 
originated  at  A  B.  C  D  is,  like  all  other  conductors,  an  obstacle  in  the 
path  which  creates  an  eddy,  so  to  speak,  in  the  ether  wave  and  reacts, 
however  minutely,  on  A  B,  because  the  movement  of  the  electric  charges 
produced  in  C  D  also  creates  an  ether  movement,  but  in  the  opposite 
direction  to  that  proceeding  from  A  B. 

21.  We  have  now  reached  a  point  where  the  electric  and  magnetic 
actions  under  discussion  are  directly  applicable  to  wireless  telegraphy, 
but  before  proceeding  with  this  subject  it  is  desirable  to  consider  more 
fully  the  action  of  A  B  on  C  D,  because  the  creation  of  electric  currents 
by  moving  or  varying  magnetic  fields,  and  vice  versa,  is  the  basis  of 
industrial  electric  power — of  that  used  in  wireless  telegraphy  as  well 
as  in  other  branches  of  electricity;  and  other  facts  or  developments  of 
this  fundamental  fact  will  appear  which  will  lead  to  a  clearer  compre- 
hension of  it. 


20 


MANUAL    OF    WIRELESS    TELEGRAPHY. 


FIG.  11. 


22.  In  fig.  11,  C  D  is  shown  parallel  to  A  B. 
If  C  D  is  slowly  revolved  around  its  own  center 
as  an  axis  the  effect  on  it  of  making,  breaking, 
or  changing  the  current  in  A  B  will  be  found  to 
decrease  until  C  D  is  at  right  angles  to  A  B, 
when  it  will  disappear  altogether.    The  lines  of 
force  are  circles  at  right  angles  to  A  B;  they  do 
not  cut  C  D  when  it  is  at  right  angles  to  A  B 
because  it  is  parallel  to  them,  and  consequently 
no  effect  is  produced. 

The  induced  effects  in  C  D  will  be  found  to 
increase  as  it  is  brought  nearer  A  B  and  to  decrease  as  it  is  removed 
from  A  B.  The  field  near  A  B  is  stronger,  and  more  lines  of  force  are 
created  there  or  dissipated  there  than  at  a  greater  distance  from  A  B — 
i.  e.,  a  greater  disturbance  in  the  ether  takes  place. 

23.  If  the  two  ends  of  C  D  (fig.  11),  are  brought  close  together,  but 
without  touching,  and  if  the  current  made  or  broken  in  A  B  is  very 
strong,  a  spark  will  pass  between  the  ends  of  C  D  at  each  make  and 
break.    If  C  D  is  separated  from  A  B  by  an  opaque,  nonmetallic  screen 
and  the  makes  or  breaks  in  A  B  are  made  to  represent  the  characters  of 
a  code,  messages  sent  in  this  code  from  A  B  can  be  received  at  C  D 
when  each  is  invisible  from  the  other.     By  the  addition  of  a  battery  to 
C  D,  similar  to  that  producing  current  in  A  B,  replies  can  be  sent,  and 
thus  a  crude  wireless  telegraphy  produced. 

24.  If  A  B  is  coiled  into  a  spiral  or  helix  and  C  D.  into  a  similar  spiral 
or  helix  (fig.  13),  the  effect  of  making,  breaking,  or  changing  the  current 
in  A  B  is  much  greater  than  where  both  wires  are  straight;  for  the 
disturbance  created  in  the  ether — that  is,  the  number  of  lines  of  force 
produced  by  the  moving  charges  in  A  B — is  equal,  for  equal  lengths  of 
the  wire,  and  since  a  greater  length  is  concentrated  in  the  same  space, 
the  number  of  lines  of  force  in  that  space,  assuming  the  current  in  the 
spiral  to  be  the  same  as  that  in  the  straight  wire,  are  correspondingly 
greater.     This  stronger  field  would  produce  an  increased  effect  on  a 
straight  wire;  but  the  length  of  C  D  is  also  concentrated.     Therefore 
the  effect  is  increased  still  more. 

25.  We  know  that  A  B  when  coiled  as  in  fig.  13  and  traversed  by  a 
current  forms  a  solenoid  (art.  8,  fig.  8).     The  space  inside  the  coil  is 
called  the  core,  and  it  has  been  assumed  that  the  surrounding  substance 
(excluding  the  ether,  which  is  present  both  in  the  interior  and  on  the 
exterior  of  all  bodies)  is  air.     It  is  found,  however,  that  if  the  core  of 
the  solenoid  is  iron,  as  in  fig.  14,  instead  of  air,  the  effect  on  C  D  is  very 
much  more  powerful — i.  e.,  the  numbers  of  lines  of  force  created  with  the 
same  current  is  very  greatly  increased. 


MANUAL    OF    WIRELESS    TELEGRAPHY. 


This  shows  that  it  is  easier  to  create  lines  of  force  in  iron  than  in  air; 
or,.  to  state  the  fact  differently,  lines  of  force  permeate  iron  more  easily 
than  they  do  air.  The  relative  ease  with  which  magnetic  lines  of  force 
are  created  in  a  substance  is  expressed  in  figures  and  called  its  magnetic 
permeability.  The  permeability  of  air  at  atmospheric  pressure  is  called 


IN  A-B  RISING^ 


unity,  and  on  that  basis  the  permeability  of  the  purest  wrought  iron  is 
3,000.    In  other  words,  within  limits  the  same  current  will  produce  3,000 
times  as  many  lines  of  force  in  iron  as  in  a  body  of  air  of  the  same 
length  and  area  of  cross  section. 
CURRENT  iNA-lB  TALLIN* 


FIG.  14. 

26.  If  the  iron  of  fig.  14  is  extended  to  include  C  D,  as  in  fig.  14a,  the 
effect  of  changes  in  A  B  is  increased  still  more,  because  in  fig.  14  the 
lines  of  force  are  partly  in  iron  and  partly  in  air,  while  in  fig.  14a  they 
have  an  iron  path  throughout,  and.  are  consequently  much  greater  in 
number.  C  D  can  also  be  placed  inside  of  A  B  or  outside  of  it,  with 
or  without  an  iron  core  (figs.  14b  and  14c).- 


MANUAL    OF    WIRELESS    TELEGRAPHY. 


FIG.  14A. — Closed-Core  Transformer  (current  in  A  B  falling) 


FIG.  14B. — Open-Core,  Step-Down  Transformer  or  Induction  Coil 
(current  in  A  B  rising). 

C 


FIG.  14c. — Air-Core,   Step-up  Transformer    (current  in  A  B   rising) 

A  C 


FIG.  14o. — Auto  Step-Down  Transformer   (current  in  A  B  rising). 


MANUAL   OF   WIRELESS   TELEGRAPHY.  23 

27.  Since  the  tendency  to  current  flow  in  C  D  is  produced  by  lines 
of  magnetic  force  cutting  C  D,  and  since  on  making  or  breaking  cur- 
rent in  A  B  each  line  of  force  cuts  C  D  once,  for  each  turn  in  C  D,  if 
the  turns  in  C  D  are  decreased  or  increased,  as  in  figs.  14b  and  14c,  the 
tendency  to  current  flow — i.  e.,  the  electro-motive  force — is  raised  or 
lowered.  From  this  fact,  and  from  the  fact  that  the  current  in  C  D  is 
opposite  in  direction  to  that  in  A  B,  the  arrangements  in  figs.  14a,  14b, 
and  14c  are  called  transformers.  Fig.  14a  is  called  a  closed-core  trans- 
former; fig.  14b  an  open-core  transformer  or  induction  coil;  fig.  14c  an 
air-core  transformer. 

Transformers  are  called  step-up  or  step-down  with  reference  to 
whether  the  number  of  turns  in  the  coil  C  D  is  greater  or  less  than 
those  in  A  B.  Fig.  14b  is  a  step-down;  fig.  14c  a  step-up  transformer. 
The  coil  A  B  is  called  the  primary  and  the  coil  C  D  the  secondary  wind- 
ing, and  where  A  B  and  C  D  have  some  turns  common  to  both,  as  in 
fig.  14d,  the  arrangement  is  called  an  auto-transformer. 


FIG.  13. 


28.  Referring  again  to  fig.  13 :  When  the  break  at  K  is  closed,  a 
current  is  started,  which  progresses  upward  through  the  coil,  the  mov- 
ing charges  composing  it  creating  a  magnetic  field  around  the  wire. 
The  lines  of  force,  as  they  expand  from  the  current  in  the  first  turn  of 
the  spiral,  cut  the  second  turn  of  A  B  in  the  same  way  that  they  cut 
C  D  a  little  later.  They  induce  a  current  in  the  second  turn  opposite 
in  direction  to  that  in  the  first  turn — i.  e.,  tending  to  stop  it.  The  same 
effect  is  produced  in  the  third  and  succeeding  turns.  In  other  words, 
the  different  parts  of  the  coil  A  B  react  on  each  other  just  as  the  coil 
C  D  reacts  on  A  B.  This  reactive  effect  of  the  turns  on  each  other 
makes  the  rise  in  current  slower  than  in  a  straight  wire,  and  is  greater 
when  the  core  of  the  coil  is  of  iron  than  when  it  is  of  air,  because  of  the 
greater  number  of  lines  of  force  produced. 


24:  MANUAL    OF    WIRELESS    TELEGEAPHY. 

29.  We  find  that  a  stronger  current  is  produced  by  the  same  battery 
in  a  short  wire  than  in  a  long  wire  of  the  same  size  and  material,  and  in 
a  thick  wire  than  in  a  thin  wire  of  the  same  length,  and  we  say  that  this 
is  due  to  the  greater  resistance  of  the  long  wire  and  of  the  thin  wire  as 
compared  with  the  short  or  with  the  thick  wire.     To  establish  the  same 
current  in  the  longer  or  the  thinner  wire  as  in  the  shorter  or  thicker 
wire  requires  a  larger  battery — that  is,  greater  E.  M.  F. 

30.  N"ow,  we  find  that  when  the  wire  is  coiled  into  a  spiral  and  a 
change  in  the  current  is  taking  place,  the  turns  react  on  each  other  and 
resist  the  change  of  the  current.     This  resistance  does  not  depend  on 
the  size  nor  the  material  of  the  wire,  but  only  on  the  amount  and  quick- 
ness of  the  change  in  the  current,  and  is  therefore  of  a  different  character 
from  the  resistance  referred  to  above.    The  resistance  of  a  wire  to  changes 
in  current  established  in  it  is  called  its  reactance,  and  during  the  change 
the  total  effect  of  the  true  resistance  and  the  reactance  is  called  the 
impedance  of  the  wire  or  circuit. 

In  circuits  having  reactance  the  production  or  progression  of  electrical 
effects  is  retarded.  It  takes  longer  to  create  a  given  current  than  in  the 
same  .length  of  straight  wire.  It  may  be  said,  therefore,  that  coiling  a 
wire  increases  its  electrical  length — i.  e.,  increases  the  time  it  takes  an 
electrical  movement  created  at  one  end  of  it  to  reach  the  other. 

The  currents  in  C  D  are  said  to  be  produced  by  the  induction  of  A  B 
on  C  D.  The  retarding  effect  of  the  coils  in  A  B  to  the  rise  and  fall  of 
current  in  A  B  is  said  to  be  due  to  the  self-induction  of  A  B.  It  has 
been  shown  that  the  amount  of  both  kinds  of  induction  depends  on  the 
shape  and  arrangement  of  both  circuits  and  the  material  (iron  or  air) 
in  and  around  them. 

METHODS    OF    PRODUCING    CURRENTS    BY    ELECTRO- MAGNETIC    INDUCTION. 

31.  The  currents  under  discussion  have  been  illustrated  as  being  pro- 
duced by  batteries  of  primary  cells,  and  for  many  purposes  these  are 
very  valuable,  but  for  the  production  of  very  powerful  electrical  effects 
advantage  is  taken  of  the  fact,  stated  in  art.  14,  that  when  magnetic 
lines  of  force  cut  or  are  cut  by  a  conductor,  electric  currents  flow  in  the 
conductor,  if  the  latter  forms  a  closed  circuit. 

The  direction  of  current  flow  can  be  determined  by  the  following  rule :  * 
(a)  An  increase  in  the  number  of  lines  of  force  embraced  by  a  circuit 
induces  a  current  in  the  opposite  direction  to  that  in  which  the  hands  of 
a  watch  move,  while  a  decrease  in  the  number  of  lines  of  force  induces  a 
current  in  the  same  direction  as  that  in  which  the  hands  of  a  watch  move, 
the  line  of  sight  being  in  both  cases  along  the  positive  direction  of  the 
lines  of  force.  (Art.  7  and  fig.  7.)  Or  rule  (b)  The  positive  direction 

*  From  Fiske's  "  Electricity  and  Electrical  Engineering." 


MANUAL   OF   WIRELESS   TELEGRAPHY.  25 

of  the  lines  of  force  is  with  the  hands  of  a  watch  when  the  current  is 
flowing  away  from  the  observer.  'And  rule  (c)  The  currents  induced  by 
moving  lines  of  force  always  tend  to  prevent  change  in  the  inducing 
current.  Induced  currents  are,  therefore,  in  the  opposite  direction  when 
the  inducing  current  is  rising  and  in  the  same  direction  as  the  inducing 
current  when  the  latter  is  falling.  (Art.  15.) 

Rule  (a)  is  illustrated  by  fig.  15;  rule  (b)  by  fig.  15a. 

From  rules  (b)  and  (c)  can  be  deduced  the  following  illustrated  in  fig. 
15b,  which  represents  a  conducting  wire  C  D  below  a  line  N"  S  represent- 
ing a  field  of  force  and  its  direction.  When  in  the  relative  positions 
shown,  movement  of  either  wire  or  line  of  force  toward  the  other  creates 
a  current  to  the  rear,  moving  either  one  away  from  the  other  creates  a 
current  to  the  front. 


FIG.    15 


It  will  be  seen  that  the  field  N"  S  can  be  revolved  through  any  angle 
around  the  wire  C  D  as  an  axis  so  as  to  be  to  the  right,  left,  or  above  or 
in  any  intermediate  position  without  changing  the  truth  of  the  above 
statement. 

These  three  rules  show  the  relation  between  what  we  call  the  positive 
direction  of  the  lines  of  magnetic  force  and  what  we  call  the  positive 
direction  of  electric  current. 

32.  No w  let  the  wire  C  D  in  fig.  11  be  bent  until  it  forms  a  rectangle, 
and  let  it  be  placed  in  the  magnetic  field  between  the  north  and  south 
poles  of  a  powerful  electro-magnet  having  an  iron  core.  By  bending  the 
core  into  the  shape  shown  in  fig.  16,  the  north  and  south  poles  are  oppo- 
site each  other  and  a  greater  number  of  lines  of  force  are  produced, 
because  the  distance  they  have  to  travel  through  the  air  is  very  much 
shortened  as  compared  with  fig.  14. 


26 


MANUAL    OF    WIRELESS    TELEGEAPHY. 


Exploration  of  the  field  in  fig.  16  by  means  of  iron  filings  or  by  means 
of  a  small  magnetic  needle  will  show  that  the  lines  of  force  extend 
directly  from  a  point  in  the  north  pole  to  the  opposite  point  in  the 
south  pole.  In  other  words,  that  they  are  straight  and  parallel  to  each 
other,  and  they  are  so  shown  in  fig.  16.  The  field  is  also  found  to  be  of 
uniform  intensity,  which  indicates  that  the  number  of  lines  of  force  are 
equally  distributed  throughout  its  area. 

Now,  if  C  D  is  moved  up  or  down  in  the  magnetic  field,  no  indica- 
tion of  a  current  can  be  perceived,  and  it  appears  that  the  statement  in 
art.  14  (that  when  magnetic  lines  of  force  cut  or  are  cut  by  a  conductor 
electric  currents  flow  in  the  conductor  if  the  latter  forms  a  closed  circuit) 
is  in  error,  but  when  we  consider  that  when  C  D  is  moved  upward  (the 


FIG.  16. 

field  being  of  uniform  intensity)  as  many  lines  of  force  are  cut  by  the 
bottom  half  as  by  the  top  half  of  C  D,  the  currents  induced  in  the  two 
halves  must  therefore  be  equal,  and  since  both  flow  to  the  rear  we  see 
that  they  neutralize  each  other,  and  the  result  is  zero.  Another  way  to 
explain  this  is  to  consider  that  portion  of  the  field  inclosed  by  C  D  as 
containing  a  certain  number  of  lines  of  force.  Those  coming  in  when 
C  D  is  moved  induce  a  current  in  one  direction,  those  going  out  induce 
a  current  in  the  opposite  direction,  and  if  as  many  come  in  as  go  out  no 
effect  is  produced. 

33.  If  C  D  were  straight,  electric  charges  would  be  produced  on  its 
ends  and  would  be  maintained  there  as  long  as  the  cutting  of  the  lines 
of  force  continued,  but  bending  it  into  a  closed  circuit  changes  conditions 
to  the  extent  that  cutting  of  lines  is  going  on  all  around  the  circuit, 
some  inducing  charges  in  one  direction,  some  in  the  other,  and  it  is 


MANUAL   OF   WIRELESS   TELEGRAPHY. 


only  when  there  is  a  preponderance  of  cutting  in  one  direction  that  a 
current  actually  flows.  This  would  occur  if  C  D  were  moved  from  a 
point  where  the  field  is  weak  to  where  it  is  stronger,  or  vice  versa,  but 
the  field  under  discussion  is  supposed  to  be  uniform.  (See  rule  a.) 

If  C  D  is  rotated  around  one  of  its  diameters  as  an  axis  (say  the  hori- 
zontal diameter  at  right  angles  to  the  lines  of  force)  when  it  is  hori- 
zontal, as  in  fig.  17,  the  lines  of  force  included  will  be  zero,  and  when 
vertical,  as  in  fig.  17a,  the  lines  of  force  included  will  be  the  maximum 
number  possible  in  that  field,  so  that  a  revolution  of  90°  will  make  an 
entire  change  in  the  number  of  lines  of  force  passing  through  the 
rectangle. 

For  instance,  if  the  revolution  is  in  the  direction  of  the  hands  of  a 
clock — i.  e.,  if  the  top  of  C  D  moves  to  the  right  (see  fig.  17a) — the 
upper  half  of  C  D  is  cutting  lines  of  force  in  the  direction  which  induces 
movements  of  electric  charges  to  the  front,  while  the  lower  half  is  cutting 
lines  of  force  in  the  direction  which  induces  movements  of  electric 
charges  to  the  rear,  so  that  an  electric  current  is  established  in  C  D  in 
the  direction  shown,  or  the  number  of  lines  of  force  included  in  C  D  is 
decreasing,  and  looking  from  N  to  S,  the  current  moves  with  the  hands 
of  a  watch. 


FIG.  17. 


'FIG.  17A. 


If  C  D's  rate  of  revolution  is  constant,  a  little  consideration  will  show 
that  when  it  has  revolved  through  90°  and  its  plane  is  horizontal  it 
is  then  moving  at  right  angles  to  the  lines  of  force,  and  consequently 
cutting  them  faster  than  when,  its  plane  being  vertical,  it  moves  parallel 
to  the  lines  of  force  for  an  instant  and  is  not  cutting  any;  also  that 
the  increase  in  the  rate  of  cutting  is  progressive  from  one  position  to  the 
other.  It  will  therefore  be  seen  that  the  electric  current  produced  is  a 
maximum  when  C  D  is  horizontal,  and  that  it  is  zero  for  an  instant 
when  C  D  is  vertical  because  during  that  instant  it  moves  parallel 
to  the  lines  of  force  and  therefore  it  cuts  none.  (No  change  in  number 
included.)  It  is  also  evident  that  the  increase  of  the  current  from  zero 
to  a  maximum  is  progressive  during  the  first  90°  of  revolution,  that  it 
then  progressively  decreases  until  C  D  has  revolved  through  180°,  and 
is  again  moving  parallel  to  the  lines  of  force  when  it  falls  to  zero. 


28  MANUAL    OF    WIRELESS    TELEGRAPHY. 

As  the  revolution  continues,  that  half  of  C  D  which  during  the  first 
half  revolution  was  cutting  lines  of  force  in  such  a  manner  as  to  induce 
a  current  to  the  front  now  cuts  them  in  such  a  manner  as  to  induce  a 
current  to  the  rear,  its  former  place  being  taken  by  what  was  originally 
the  lower  half,  so  that  the  direction  of  current  in  C  D  is  reversed. 
(Eule  c.) 

Another  maximum  rate  of  cutting  lines  of  force  and  consequent  maxi- 
mum of  current  is  produced  when  C  D  has  revolved  through  270°.  The 
current  progressively  increases  from  180°  to  270°  and  then  decreases 
until  when  the  original  conditions  are  restored  by  the  completion  of  one 
revolution  the  current  has  again  fallen  to  zero. 

From  the  above  and  from  an  inspection  of  fig.  17a  it  will  be  seen  that 
current  is  always  flowing  to  the  front  in  that  half  of  C  D  which  is  going 
down  to  the  right  and  to  the  rear  in  the  half  going  up  on  the  left,  and 
that  each  half  revolution  the  current  changes  in  direction.  Such  a  cur- 
rent is  called  an  alternating  current. 


FIG.  18. 


34.  This  can  be  shown  graphically  in  fig.  18,  where  the  rate  of  cut- 
ting and  therefore  the  rate  of  change  of  number  of  lines  included  in  the 
circuit  at  different  equidistant  points  in  one  revolution  is  represented  by 
equidistant  vertical  lines  proportional  to  the  cutting  rate,  and  conse- 
quently to-  the  current  strength.  Vertical  lines  above  the  horizontal  line 
represent  current  strength  in  one  direction  and  below  it  current  strength 
in  the  opposite  direction.  A  regular  curve  is  produced  by  joining  the 
tops  of  these  lines.  This  curve  is  the  curve  of  sines,  because  the  rate  of 
cutting  and  the  strength  of  the  induced  current  are  proportional  to  the 
sine  of  the  angle  of  revolution.* 

*  Since  the  lines  of  force  are  horizontal,  the  number  cut  during  the  revolu- 
tion of  C  D  through  any  angle  is  proportional  to  the  vertical  movement  of  the 
extremity  of  the  radius  of  C  D  which  generates  the  angles.  The  amount  of 
this  vertical  movement  is  the  sine  of  the  angle,  and  therefore  the  induced 
current  is  proportional  to  the  sine  of  the  angle. 


MANUAL    OF    WIRELESS    TELEGRAPHY.  29 

35.  If  C  D  instead  of  forming  a  closed  circuit  entirely  in  the  mag- 
netic field  has  its  ends  connected  to  two  rings  which  revolve  with  it  and 
touching  these  rings  are  the  ends  of  a  coiled  wire  (E  F,  fig.  19),  the 


FIG,  19 


currents  induced  in  C  D  also  flow  through  E  F  and  make  of  it  a  sole- 
noid whose  strength  varies  with  the  strength  of  the  current  and  whose 
polarity  reverses  with  the  reversal  of  the  current.  If  a  small  magnetic 
needle  were  pivoted  in  E  F,  its  direction  would  tend  to  change  with  each 
reversal  of  the  current,  and  it  can  thus  be  made  to  indicate  both  the 
direction  and  the  amount  of  current  flowing  through  the  coil  E  F.  Such 
an  instrument  is  called  a  galvanometer. 

The  currents  in  the  coil  E  F  are  supplied  from  C  D,  and  they  are 
induced  in  C  D  by  its  movements  in  a  magnetic  field.  C  D  has  become 
a  source  of  electricity  like  the  battery  in  A  B.  E  F  corresponds  to  the 
coil  A  B  in  fig.  13,  and  the  rise  and  fall  of  current  in  E  F  will  produce 
a  rise  and  fall  of  current  in  another  coil  near  it,  just  as  the  make  and 
break  at  K  in  fig.  13  induces  momentary  currents  in  C  D. 

The  currents  in  C  D,  fig.  13,  were  induced  by  interrupted  current. 
Those  induced  by  E  F  in  coils  near  it  are  induced  by  alternate  current. 
Interrupted  current  was  used  almost  entirely  in  wireless  telegraphy  in 
its  earlier  development.  It  has  now  been  replaced  by  alternate  current. 

36.  It  only  remains  now  to  make  C  D  produce  the  magnetic  field 
in  which  it  revolves,  and  we  can  dispense  entirely  with  the  primary 
battery  in  A  B.  This  can  be  done  as  follows : 

In  fig.  20  instead  of  having  each 
end  of  C  D  connected  to  a  ring  of 
conducting  material,  as  in  fig.  19, 
one  ring  is  removed  and  the  other 
split  into  two  equal  parts  and  an  end 
of  C  D  connected  to  each  part,  the 
ends  of  E  F  being  adjusted  so  that  as 
the  split  ring  revolves  with  C  D  one 
end  of  E  F  is  always  connected  FIG.  20. 


30 


MANUAL    OF    WIRELESS    TELEGRAPHY. 


through  the  split  ring  with  that  half  of  C  D  in  which  the  current  is  flow- 
ing to  the  front  and  the  other  end  to  that  half  in  which  the  current  is 
flowing  to  the  rear.  This  arrangement  makes  the  current  in  E  F  always 
flow  in  the  same  direction.  It  rises  and  falls  with  the  current  in  C  D,  but 
does  not  reverse,  because  just  as  the  current  reverses  in  C  D,  E  F  changes 
ends,  so  to. speak,  by  breaking  connection  with  one  half  of  the  split  ring 
and  making  connection  with  the  other.  The  current  in  E  F  is  now  said 
to  be  a  pulsating  instead  of  an  alternating  current,  and  the  change  can  be 
graphically  represented  by  transferring  the  part  of  the  curve  below  the 
line  in  fig.  18  to  a  corresponding  position  above  it,  as  in  fig.  18a. 


\ 


FIG.  ISA. 

The  alternating  current  in  CD  is  said  to  be  rectified  into  a  direct 
current  in  E  F.  The  split  ring  by  means  of  which  it  is  rectified  is  called 
a  commutator,  and  the  entire  apparatus  (either  with  or  without  a  com- 
mutator), a  dynamo. 

37.  With  a  single  coil,  C  D,  rotating  in  the  magnetic  field  the  current 
in  E  F  can  be  made  to  flow  always  in  the  same  direction,  but  in  order  to 
make  it  constant  a  large  number  of  coils,  equally  spaced,  must  be  used, 
so  that  one  of  them  is  passing  through  the  position  (horizontal)  in 
which  maximum  current  is  produced  practically  all  the  time.  If  there 
were  10  such  coils,  each  connected  to  its  own  split  ring  (fig.  21),  and 
all  connected  to  E  F,  the  currents  in  each  would  overlap,  so  that  the 
resultant  current  in  E  F  to  another  scale  might  be  indicated  by  a  line 
joining  the  highest  point  of  each  (fig.  18b).  In  other  words  the  current 
in  E  F  is  practically  constant. 


FIG.  18s. 

The  revolving  coils  are  held  in  place  on  a  cylindrical  drum  or  ring 
and  the  whole  is  called  an  armature.  If  this  ring  is  made  of  iron  the 
strength  of  the  magnetic  field  is  much  increased,  because  the  iron  affords 
a  path  for  the  lines  of  force  from  one  pole  to  the  other  and  thereby 
lessens  the  distance  through  which  they  have  to  pass  in  the  air.  (See 
art.  25.) 


MANUAL    OF    WIRELESS    TELEGRAPHY. 


31 


The  tendency  to  current  flow  in  C  D  created  by  cutting  lines  of  force 
is  called  the  electromotive  force  in  C  D  (see  art.  3),  and  is  found  to 
depend  on  the  number  of  lines  cut  in  a  given  time,  so  that  the  faster 
C  D  revolves,  and  the  stronger  the  magnetic  field,  the  greater  the  electro- 
motive force  and  the  greater  the  current  produced  in  any  given  circuit. 
Now,  if  the  current  induced  in  C  D,  instead  of  all  flowing  through  E  F, 
is  divided,  so  that  part  of  it  flows  around  the  core  of  the  electro-magnet 
(fig.  21),  this  current  can  take  the  place  of  that  produced  by  the  battery 
in  A  B  and  the  battery  can  be  dispensed  with. 


FIG.  21. 

38.  In  art,  6  it  is  stated  that  wrought  or  soft  iron  can  be  magnetized, 
but  only  retains  its  magnetism  while  under  the  influence  of  the  magnet- 
izing force.  Steel  or  hard  iron  once  magnetized  retains  its  magnetiza- 
tion permanently  and  special  means  to  demagnetize  it  are  required.  It 
is  found  that  electro-magnets  with  soft-iron  cores  can  be  made  more 
powerful  (i.  e.,  will  give  a  stronger  field)  than  if  the  cores  are  of  steel, 
and  that  electro-magnets  with  either  kind  of  core  can  be  made  to  give 
much  stronger  fields  than  any  permanent  magnet.  Also,  that  soft-iron 
cores  retain  a  very  small  part  of  their  magnetism  and  polarity  when  the 
current  i&  broken,  so  that,  if  the  magnet  poles  between  which  C  D 
revolves  are  made  of  the  most  efficient  material  (wrought  iron  or  mild 
steel  containing  no  phosphorus),  when  C  D  stops  they  still  retain  their 
polarity  in  a  slight  degree.  .  . 

When  C  D  starts  to  revolve  again  the  weak  field  generates  a  small  cur- 
rent in  C  D,  which  sends  this  current  through  the  wire  around  the  poles ; 
this  current  increases  the  strength  of  the  poles  and  consequently  of  the 
field  which  increases  the  current  in  C  D  and  so  on.  This  is  called 
generating  or  building  up,  and  continues  until  the  limit  of  the  power 
moving  C  D  in  the  continually  strengthening  field  is  reached,  or  until 
the  iron  core  is  saturated,  in  which  condition  no  increase  of  current  will 
increase  the  field. 


32  MANUAL    OF    WIRELESS    TELEGRAPHY. 

39.  When  alternating  current  is  desired,  a  dynamo,  in  order  to  be 
self-exciting,  i.  e.,  to  produce  its  own  field,  must  have  part  of  its  cur- 
rent rectified  by  means  of  a  commutator.     It  is  more  usual,  however, 
to  drive  a  small  direct-current  dynamo  by  means  of  the  same  power 
which  drives  the  larger  one,  the  current  from  the  small  dynamo  being 
used  to  create  the  magnetic  field  in  the  larger  one.     Such  a  machine  is 
called  an  exciter. 

40.  The  fact  that  magnet  poles  of  unlike  polarity  attract  each  other 
(art.  6)   applies  to  electro-magnets,  with  or  without  iron  cores,  as  well 
as  to  permanent  magnets.     Hence  two  electro-magnets  placed  as  in  fig. 
13  will  attract  or  repel  each  other  according  to  their  polarity.    Each  line 
of  force  apparently  tends  to  contract  in  the  direction  of  its  length,  and 
by  so  doing  exerts  a  mechanical  pull  on  the  conductors  which  it  sur- 
rounds. 

The  same  effect  is  observed  between  a  magnet  and  a  wire  carrying  a 
current  (which,  as  we  know,  has  a  magnetic  field  around  it)  and  between 
two  wires,  each  carrying  a  current.  They  actually  pull  or  push  each 
other  according  to  the  quality  of  their  magnetism,  which  is  determined 
by  the  direction  of  the  current. 

41.  If  in  fig.  21  the  armature  instead  of  being  revolved  to  the  right  by 
some  outside  agency,  is  supplied  with  a  current  flowing  through  it  in  the 
same  direction  as  the  current  it  generates,  it  will  revolve  to  the  left. 

The  current  flowing  to  the  front  in  the  winding  of  the  right  half  of 
the  armature  and  to  the  rear  in  the  winding  of  the  left  half  makes  of  it 
an  electro-magnet  with  a  north  pole  at  the  bottom  and  a  south  pole  at  the 
top.  The  revolution  is  caused  by  the  attraction  of  the  north  pole  of  the 
armature  by  the  south  pole  of  the  field  magnet,  and  its  repulsion. by  the 
north  pole  of  the  field  magnet,  This  action  is  reversed  in  the  south  pole 
of  the  armature. 

The  movement  will  be  continuous,  because,  as  the  top  of  the  arma- 
ture moves  toward  the  north  pole  of  the  field  magnet,  the  commutator 
acts  to  maintain  the  flow  of  current  as  before,  and  the  consequent  arma- 
ture poles  are  always  at  the  top  and  bottom  halfway  between  the  field 
magnets. 

The  armature  thus  creates  a  current  when  made  to  revolve,  and 
revolves  when  supplied  with  current. 

In  the  first  instance  we  have  seen  that  the  entire  machine  is  called 
a  dynamo;  in  the  second  it  is  called  a  motor.  Every  dynamo  will  run 
as  a  motor  if  supplied  with  current.  Every  motor  will  act  as  a  generator 
or  dynamo  if  made  to  revolve  in  its  own  field. 

The  motor  can  be  made  to  drive  another  armature  in  another  field. 
Such  a  machine  is  called  a  motor-generator.  It  can  be  run  with  direct 
or  alternating  currents  and  made  to  generate  direct  or  alternating  cur- 


MANUAL    OF    WIRELESS    TELEGRAPHY.  33 

rents  of  a  higher  or  lower  E.  M.  F.  For  this  reason  it  is  sometimes 
called  a  rotary  transformer,  as  distinguished  from  the  stationary  trans- 
formers already  described. 

ELECTRIC  AND  MAGNETIC  FIELDS.      / 

42.  Electricit}^  produced  by  friction  (art.  1)  is  sometimes  called  fric- 
tional  electricity;  by  primary  batteries,  voltaic  electricity;  by  electro- 
magnetic  induction,   dynamic  electricity.     But  however  produced   and 
transformed,,  all  kinds  of  electricity  are  identical,  and  the  same  is  true 
of   all   kinds   of   magnetism.      Wherever   there   is    an    electric    charge, 
stationary  or  moving,  emanating  from  the  charge  are  electric  lines  of 
force  which  end  at  other  electric  charges.     Wherever  there  are  moving 
electric  charges   (currents)   there  are  magnetic  lines  of  force  also,  and 
these  magnetic  lines  of  force  are  always  at  right  angles  to  the  direction 
of  the  motion  of  the  charges  and  to  the  electric  lines  of  force  proceed- 
ing from  them. 

And,  finally,  motion,  or  state  of  strain  in  the  ether,  which  these  lines 
of  force  represent,  travels  with  the  speed  of  light,  and  the  fields  of  force, 
while  more  pronounced  and  therefore  more  easily  detected  near  the 
moving  charges,  are  really  all  pervasive.  They  have  no  limits. 

43.  Imagine  a  disturbance — say  an  expansion  of  a  gas — to  take  place 
in  the  center  of  an  immense  rubber  ball.    A  wave  of  tension,  which  be- 
comes less  as  its  distance  from  the  center  increases,  progresses  outward 
to  the  farthest  confines  of  the  ball.    When  the  gas  contracts,  a  wave  of 
contraction,    also    starting   from    the   center,    and    decreasing   with    its 
distance  from  the  center,  progresses  outward  to  the  farthest  confines  of 
the  ball.     If  expansion  and  contraction  are  equal  the  ball's  former  state 
of  equilibrium  is  restored. 

In  this  way  it  can  be  imagined  that  starting  a  current  produces  a 
state  of  strain  in  the  ether  or  stretches  it  in  one  direction;  stopping  it 
releases  the  strain.  Action  in  both  cases  starts  at  the  point  where  the 
current  is  produced  and  progresses  outward  with  the  speed  of  light,  and 
a  little  consideration  will  show  that  it  can  have  no  limit,  though  it  soon 
ceases  to  be  perceptible  except  under  certain  conditions,  to  be  later 
described. 

The  function  of  wireless  telegraphy  is  to  produce  these  ether  move- 
ments at  will. 

ELECTRIC   CAPACITY. 

44.  We  can  produce  momentary  currents  in  conductors,  whether  open 
or  closed,  by  the  cutting  of  lines  of  force,  and  the  evidences  of  electrifi- 
cation are  most  pronounced  at  the  ends  of  an  open  conductor,  but  these 
disappear  as  soon  as  the  cutting  of  lines  of  force  ceases.    We  find,  how- 
ever, that  electrification  of  amber,  glass,  silk,  and  other  bodies  remains 


34  MANUAL   OF   WIRELESS    TELEGRAPHY. 

after  the  rubbing  ceases,  and  if  glass  plates  or  other  nonconductors  be 
connected  to  the  ends  of  a  conductor  in  which  an  E.  M.  F.  is  being 
generated,  so  that  connection  is  made  all  over  the  surface  of  the  glass 
(as  it  is  when  rubbed),  the  glass  when  separated  from  the  conductor 
will  be  found  to  be  electrically  charged  the  same  as  when  electrified  by 
rubbing.  When  two  plates  oppositely  charged  (art.  1)  are  connected 
through  wires  leading  to  a  galvanometer,  the  amount  of  deflection  of  the 
galvanometer  needle  (caused  by  the  magnetic  field  of  the  momentary 
current  created  as  the  charges  unite  and  neutralize  each  other)  is  a 
measure  of  the  quantity  of  electricity  on  each  plate. 

In  testing  plates  of  different  sizes,  shapes,  and  materials,  charged  to 
the  same  potential  by  being  connected  to  the  poles  of  the  same  source 
of  electricity,  it  is  found  that 'different  values  of  the  throw  of  the  gal- 
vanometer needle  are  produced.  Other  conditions  being  equal,  plates 
having  the  greatest  amount  of  surface  are  found  to  have  the  largest 
capacity.  Plates  of  the  same  capacity  will  give  a  larger  throw  of  the 
galvanometer  when  charged  from  a  source  of  high  than  a  source  of  low 
potential,  so  that  the  amount  of  electricity  stored  in  an  electrified  body 
depends  on  its  potential  as  well  as  on  its  capacity. 

45.  If  two  plates,  oppositely  charged  by  being  connected  to  the  poles 
of  a  battery,  as  in  fig.  22,  or  to  the  terminals  of  a  dynamo  or  transformer 
are  discharged  by  being  connected  through  a  galvanometer,  the  throw 
of  the  galvanometer  will  not  be  as  great  as  if  the  same  plates,  charged 
to  the  same  potential  by  the  same  battery  as  in  fig.  22a,  are  discharged 
through  the  same  galvanometer.  By  being  brought  closer  together  the 
plates  seem  to  have  their  capacity  increased.  It  takes  a  greater  amount 
of  electricity  to  bring  them  to  the  same  potential  than  when  farther 
apart.  If  two  plates  charged  at  a  distance  from  each  other,  as  in  fig.  22, 


FIG.  22. 

and  then  disconnected  from  the  battery  are  brought  to  the  position  shown 
in  fig.  22a,  their  potential,  as  measured  by  an  electroscope,  is  found  to 
be  lowered.  The  electricity  is  said  to  be  condensed  by  the  approach  of 
the  plates,  and  such  an  arrangement  is  termed  a  condenser,  a  somewhat 
misleading  term,  but  one  generally  used.  . 

This  is  analogous  to  the  increased  strength  of  magnetic  field  produced 
by  shortening  the  magnetic  circuit  while  retaining  the  same  magnetizing 


MANUAL    OF    WIRELESS    TELEGRAPHY.  35 

force.  In  both  cases  the  field  of  force  represents  stored  energy  which  can 
be  made  to  reappear  in  the  discharge  of  the  condenser  or  the  dissipation 
of  the  field. 

The  two  plates  can  be  reduced  to  one  if  of  nonconducting  material, 
but  since  a  nonconductor  can  not  transmit  electric  charges,  in  order  to 
utilize  the  two  surfaces  of  the  plate,  each  must  be  covered  with  a  con- 
ductor which  will  permit  the  charges  to  distribute  themselves  over  its 
area. 

ELECTRIC    INDUCTION. 

46.  Electric  lines   of  force  permeate   a   nonconductor — i.   e.,   electric 
induction  takes  place  through  it, — in  a  way  analogous  to  that  in  which 
magnetic  induction  takes  place  through  iron  or  air. 

The  permeability  of  air  for  magnetic  induction  is  taken  as  a  standard 
and  called  unity.  (See  art.  25.) 

Its  permeability  for  electric  induction  is  also  taken  as  a  standard  and 
called  unity,  and  as  we  find  that  iron,  nickel,  cobalt,  and  oxygen  have  a 
greater  magnetic  permeability  than  air,  so  we  find  that  glass,  beeswax, 
paraffin,  nearly  all  kinds  of  oil,  and  indeed  most  bodies  we  call  insulators, 
have  a  greater  electric  permeability  than  air.  The  quality  of  a  body  as 
compared  with  air  in  this  respect  is  called  its  specific  inductive  capacity, 
and  bodies  when  considered  with  reference  to  electric  induction  through 
them  are  called  dielectrics.  (Art.  2.) 

It  is  found  that  the  best  quality  of  glass  has  nine  times  the  specific 
inductive  capacity  of  air.  This  means  that  when  subjected  to  the  same 
potential,  the  electric  field,  when  this  glass  is  the  dielectric,  is  nine  times 
as  strong  as  that  created  when  the  medium  intervening  between  the 
charges  is  air,  it  requires  nine  times  as  much  work  to  create  it,  and  its 
discharge  can  do  nine  times  as  much  work. 

47.  Bodies  such  as  iron  or  nickel  through  which  magnetic  induction 
is   taking   place   are   found   to   change   slightly   in   shape,   and   sudden 
changes   in  the  induction  or  lines  of  force  permeating  them  produce 
slight  sounds.     The   action  is  also  accompanied  by  the  production  of 
heat,  but  as  the  magnetizing  force   (magneto-motive  force)    increases, 
the  lines  of  force  tend  to  reach  a  maximum  which  no  increase  of  mag- 
netizing force  will  increase.     When  in  this  condition  the  magnetized 
body  is  said  to  be  saturated.     There  is,  however,  apparently  no  limit  to 
the  magnetization  of  air. 

In  the  same  way  bodies  (dielectrics)  through  which  electric  induction 
is  taking  place  are  found  to  change  (enlarge)  slightly  in  shape,  but 
increase  of  electro-motive  force  (in  this  case  potential)  does  not  appear 
to  tend  to  a  maximum  of  electric  induction.  The  physical  strain  on  *  the 
dielectric,  however,  continues  to  increase  and  finally  reaches  a  point 
where  it  pierces  or  ruptures  the  dielectric,  the  action  being  accompanied 


36  MANUAL    OP    WIRELESS    TELEGRAPHY. 

by  a  sharp  crackling  sound  and  by  the  production  of  light  and  heat, 
which  we  call  an  electric  spark.  If  the  dielectric  is  air  or  a  liquid,  the 
rupture  is  immediately  repaired  by  the  action  of  the  surrounding  sub- 
stance on  that  heated  by  the  passage  of  the  spark ;  but  if  the  dielectric  is 
a  solid  the  rupture  is  permanent.  Magnetization  is  limited  by  satura- 
tion. The  limit  of  electrification  is  marked  by  rupture.  The  electric 
charges  are  found  to  have  been  dissipated  after  the  spark  has  passed. 
The  condenser  is  said  to  be  discharged.  If  the  oppositely  charged  plates 
are  discharged  without  sparking,  a  slight  sound  is  produced  if  the 
dielectric  is  glass.  This  is  analogous  to  the  minute  sounds  given  out  by 
magnets  when  magnetized  or  demagnetized  suddenly. 

Magnetization  or  electrification  seems  to  consist  of  forcing  to  point  in 
the  same  direction  the  magnetic  or  electric  polarities  of  the  molecules 
of  a  substance. 

We  have  seen  that  the  capacity  of  an  electrified  body  depends  on  the 
area  of  its  electrified  surface,  on  the  nearness  of  its  charge  to  charges 
of  opposite  sign,  and  on  the  material  of  the  dielectric — i.  e.,  the  sub- 
stance intervening  between  the  charges. 

ELECTRIC   CONDENSERS. 

48.  Bodies  capable  of  being  electrified  and  arranged  so  as  to  present 
a  large  capacity  in  a  small  space  are  frequently  called  simply  capacities, 
but  this  term  is  misleading,  and  though  the  term  condenser  is  not 
entirely  satisfactory  it  will  be  used.  The  total  charge  in  a  condenser 
depends  on  its  potential  as  well  as  its  capacity.  Its  potential  depends 
on  the  potential  of  the  source  of  electricity  only,  but  its  capacity,  as 
stated  above,  depends  on  its  size,  material,  and  arrangement. 

Condenser  capacities  may  be  said  to  be  related  to  each  other  in  the 
same  way  as  rubber  bags  inflated  by  gas.  A  large  bag  charged  to  a 
given  pressure  contains  more  gas  than  a  small  bag  charged  to  the  same 
pressure.  The  gas  in  the  large  bag  is  making  no  greater  effort  to  escape 
per  square  inch  (i.  e.,  has  no  higher  potential)  than  the  gas  in  the 
small  bag ;  but  it  requires  a  longer  time  and  more  gas  to  charge  the  large 
bag  than  the  small  one. 

So  when  connected  to  the  same  source  of  electricity  it  requires  a 
longer  time  to  charge  a  condenser  of  large  capacity  to  a  given  potential 
than  it  does  to  charge  a  small  one  to  the  same  potential,  and  its  power 
to  do  work  is  correspondingly  greater. 

In  the  same  way  it  requires  a  longer  time  to  create  the  magnetic  field 
of  a  large  electro-magnet  than  that  of  a  small  one,  and  a  stronger  mag- 
netic field  (within  limits)  is  created  by  a  large  current  than  by  a  small 
one  under  the  same  conditions,  and  the  energy  stored  in  the  strong  field 
and  its  power  to  do  work  is  correspondingly  greater. 


MANUAL    OF   WIRELESS    TELEGRAPHY.  37 

49.  It  is  evident  that  a  close  analogy  can  be  drawn  between  the  electric 
field  in  a  condenser  and  the  magnetic  field  around  an  electro-magnet. 
We  have  seen  that  any  movement  of  either  field  creates  the  other;  that 
they  can  exist  independently  only  in  a  static  condition;  that,  though 
they  have  no  limits,  the  center  of  effort,  the  point  of  greatest  activity  in 
each,  is  at  the  body  which  we  consider  electrified  or  magnetized;  that 
bodies  differ  in  their  qualities  in  these  respects;  that  an  actual  physical 
change  takes  place  in  the  dielectric  when  electrified  and  in  the  iron  or 
nickel  when  magnetized,  and,  finally,  that  both  electric  and  magnetic 
fields  represent  stored  energy  in  an  infinitely  elastic  medium,  and  we 
shall  see  that  this  medium,  on  account  of  its  elasticity,  vibrates  and 
oscillates  when  either  an  electric  or  a,  magnetic  field  is  suddenly  created 
or  destroyed  in  it. 

50.  The  most  common  and  best  known  form  of  condenser  is  the  Leyden 
jar,  which  consists  of  an  inner  and  outer  coating  or  film  of  tin  foil  or 
copper  on  a  glass  jar,  the  glass  being  the  dielectric.     Electric  induction 
takes  place  through  the  glass  and  the  energy  is  stored  in  the  electric  field, 
the  tin  foil  merely   serving  to   increase  the   area  over  which  electric 
induction  takes  place,  and  hence  the  capacity  of  the  condenser. 

Condensers  are  often  made  up  of  a  large  number  of  interlaced  plates 
or  films  of  conducting  material,  having  between  them  for  a  dielectric 

FIXED  CONDENSER  VARIABLE  CONDENSER 


HI- 


PIG.  23.  FIG.  2  3  A.  FIG.  23s. 

larger  pieces  of  glass,  mica,  or  oiled  paper,  alternate  plates  being  simi- 
larly charged.  Condensers  are  represented  either  as  in  fig.  23  or  fig.  23a. 
They  will  be  represented  in  this  book  as  in  fig.  23.  Condensers  are  also 
made  in  which  the  relative  position  of  the  plates,  and  therefore  the 
capacity,  can  be  varied  at  will.  These  are  called  variable  condensers, 
and  will  be  represented  as  in  fig.  23b.  In  variable  condensers  the 
dielectric  may  be  glass,  air,  oil,  mica,  or  paper. 

DISCHARGE   OF   CONDENSERS. 

51.  If,  after  being  charged  by  connecting  the  inner  coating  to  one 
pole  of  a  source  of  electricity  and  the  outer  coating  to  the  other,  the  two 
coatings  are  connected  by  means  of  a  conducting  wire  the  charges 
neutralize  each  other  and  the  condenser  is  said  to  be  discharged.  The 
discharge  of  a  condenser  being  a  movement  of  electricity  creates  a  cur- 
rent and  consequently  a  magnetic  field  around  the  wire  through  which 
the  discharge  takes  place. 


38  MANUAL    OP   WIRELESS    TELEGRAPHY. 

If  the  potential  is  high  enough  the  condenser  can  be  discharged  with- 
out actually  connecting  the  two  coatings,  for  when  the  opposite  ends  of 
wires  connected  to  them  are  brought  within  a  certain  distance  of  each 
other  sparks  will  pass,  and  the  condenser  will  be  found  to  be  discharged, 
the  same  as  if  the  wires  were  actually  connected.  The  charges  unite  by 
rupturing  the  air  dielectric.  The  energy  stored  in  the  electric  field 
appears  as  sound,  light,  heat,  and  other  invisible  ether  vibrations. 

This  spark  discharge  is  found  when  analyzed  to  consist  usually  of 
several  sparks,  passing  first  in  one  direction,  then  in  the  other.  Each 
condenser  coating  is  charged  positively  and  negatively  in  rapid  succes- 
sion, each  charge  being  somewhat  less  than  the  preceding  until  the 
entire  energy  of  the  original  charge  is  dissipated.  This  form  of  con- 
denser discharge  is  oscillating.  The  released  charge  acts  like  a  released 
musical  string  which  vibrates  until  its  energy  is  dissipated,  and  as  the 
same  string  gives  out  the  same  note,  whether  stretched  strongly  or  only 
a  little,  so  a  condenser  when  discharged  through  the  same  wire  always 
vibrates  or  oscillates  in  the  same  period,  regardless  of  its  potential.  Just 
as  the  note  given  out  by  the  string  depends  on  its  material  and  length, 
so  the  rate  of  vibration  of  a  condenser  depends  on  its  capacity,  which,  as 
we  have  seen,  depends  on  its  material  and  arrangement. 

52.  Another  illustration  of  oscillatory  condenser  action  can  be  given: 
Let  fig.  24  represent  two  glass  vessels  connected  by  a  U  tube  with  a 
stopcock  at  the  bottom  of  the  tube.  One  vessel  is  filled  with  water  and 
the  other 'empty.  If  the  U  tube  is  large  enough  to  permit  free  passage 
of  the  water,  when  the  stopcock  is  opened  quickly  the  pressure  in  the 
filled  vessel  will  cause  a  sudden  rush  of  water  up  the  other  side  of  the 
tube  into  the  empty  vessel,  which  will  continue  until  it  has  reached 
nearly  the  same  height  as  before  (fig.  24a).  It  will  then  rush  ba'dv  into 
the  first  vessel,  and  so  on,  reaching  a  little  lower  level  each  time  until 
equilibrium  is  reached  at  the  same  level  in  both  vessels  (fig.  24b) . 

The  only  action  which  prevents  the  oscillation  from  being  continuous 
is  friction  of  the  water  on  the  walls  of  the  tube  and  internal  friction 
between  its  molecules. 

Released  condenser  charges  would  also  continue  to.  oscillate  indefi- 
nitely if  it  were  not  for  the  resistance  in  the  discharging  wires  and  in 
the  dielectric  and  the  sound  and  light  produced  by  the  spark.  These 
absorb  the  energy  of  the  charge,  and,  being  relatively  large,  a  position 
of  equilibrium  is  reached  after  a  few  oscillations. 

If  the  U  tube  in  fig.  24  is  very  small  or  the  stopcock  only  slightly 
opened  the  water  will  gradually  rise  on  the  other  side  and  will  finally 
reach  a  position  of  equilibrium  without  any  oscillation,  and  it  is  found 
that  if  the  condenser  discharge  takes  place  through  a  long  thin  wire 
instead  of  a  thick  one  the  condenser  is  slowly  discharged  through  it 
without  anv  oscillation. 


MANUAL    OF    WIRELESS    TELEGRAPHY. 


39 


53.  The  oscillation  of  the  water  in  fig.  24  is  due  to  its  inertia.  Inertia 
is  a  property  of  all  bodies  and  is  in  amount  proportional  to  their  weight. 
It  is  represented  by  their  resistance  to  change  of  condition,  either  of 
motion  or  of  rest. 

The  water  in  the  first  vessel  falls  by  the  action  of  gravity.  Once  in 
motion  its  inertia  (resistance  to  change  of  condition)  causes  it  to  rise 
on  the  opposite  side  against  the  action  of  gravity.  When  gravity  has 
overcome  its  inertia  it  falls  again  by  gravity  and  is  carried  on  by  inertia. 


FIG.  24. 


FIG.  24A. 


FIG.  24e. 

It  continues  to  overshoot  the  mark,  so  to  speak,  until  friction,  internal 
and  external,  brings  it  to  rest. 

Though  the  electric  charges  on  condenser  coatings  appear  to  be  inde- 
pendent of  gravity,  they  do  possess  inertia,  as  is  shown  by  their  resist- 
ance to  change  of  direction  and  by  their  oscillatory  movements. 

54.  Let  us  consider  a  charged  condenser  (fig.  25)  discharged  through 
a  thick  wire  connecting  the  coatings.  A  break  in  the  wire  prevents  the 
discharge  until  the  potential  is  high  enough  to  cause  sparks  to  cross  the 
break.  One  condenser  coating  before  discharge  is  at  a  certain  positive 
potential,  the  other  at  an  equal  negative  potential.  Both  discharge 
through  the  wire  in  the  same  time,  and  when  they  have  reached  zero 
potential  the  electric  field  has  been  dissipated,  but  the  moving  charges 


40  MANUAL    OF    WIRELESS    TELEGRAPHY. 

in  the  wires  have  induced  a  magnetic  field  around  the  wire.  The 
strength  of  this  magnetic  field  depends  on  the  amount  of  the  moving 
charges,  i.  e.,  the  strength  of  the  current.,  and  on  the  self-induction 
(art.  30)  of  the  wire  which,  as  we  know,  depends  on  its  shape  and  the 
material  (air  or  iron)  in  which  the  magnetic  field  is  created.  All  the 
energy  (except  that  lost  by  friction)  which  was  stored  in  the  electric 
field  is  now  in  the  magnetic  field  (fig.  25a).  The  magnetic  field,  having 
no  continuous  source  of  magneto-motive  force  (current)  to  maintain  it, 
collapses  on  the  wire,  producing  movements  of  the  electric  charges  into 
the  condenser  coatings,  which  now  become  charged  in  the  opposite  sense 
(fig.  25b).  The  electric  field  is  again  set  up,  containing  all  the  remain- 
ing energy,  and  the  magnetic  field  disappears  until  the  charges  again 
move  toward  each  other. 

QSOLLATIWG  CONDENSER  DISCHARGE 


AT  START  ENERGY  ALL  ELECTRIC.   END  OF  QUARTER  CYCLE  ENERGY 
,  ALL  MAGNETIC. 

FIG.  25.  FIG.  25A. 


ENERGY  ALL  ELECTRIC  ENERGY  A'  L  MAGNETIC          ENERGY  ALL  ELECTRIC 

REVERSED-  REVERSED.  LESS  IN  AMOUNT. 

FIG.-  25B.  FIG.  25c.  FIG.  25D. 

The  attraction  of  the  unlike  charges  for  each  other  is  analogous  to 
the  attraction  of  gravity  for  the  water  in  fig.  24,  and  the  magnetic  field 
caused  by  the  self-induction  of  the  moving  charges  is  analogous  to  the 
inertia  of  the  water,  which  makes  it  rise  in  the  second  vessel,  because 
the  collapse  of  this  magnetic  field  charges  the  condenser  in  the  opposite 
sense,  and  for  this  reason  self-induction  is  sometimes  called  electro- 
magnetic inertia.  , 

From  the  foregoing  illustration  of  what  appears  to  take  place  during 
the  oscillating  discharge  of  a  condenser  we  see  that  the  energy  before 
an  oscillation  begins  is  all  electric.  At  the  end  of  the  first  quarter  of  a 
cycle  it  is  all  magnetic.  At  the  end  of  a  half  cycle  it  is  all  electric,  but 
in  the  opposite  sense.  At  the  end  of  three-quarters  of  a  cycle  it  is  all 
magnetic,  but  with  the  direction  of  the  lines  of  force  reversed.  At  the 
end  of  a  complete  cycle  or  oscillation  the  energy  is  all  electric  again 


MANUAL    OF    WIRELESS    TELEGRAPHY.  41 

(figs.  25a,  25b,  25c,  25d)  and  in  the  original  sense,  but  less  in  amount 
on  account  of  the  losses  which  have  taken  place  during  the  transforma- 
tions and  which  are  shown  by  the  heating  of  the  condenser  and  the  wires 
(and  the  sound  and  light  produced  by  the  spark  if  the  oscillations  take 
place  through  a  spark  gap).  At  all  intermediate  points  of  a  cycle  the 
energy  is  partly  electric  and  partly  magnetic. 

55.  A  complete  oscillation  or  cycle  is  made  up  of  two  alternations. 
The  highest  potential  reached  during  an  oscillation  is  called  the  ampli- 
tude of  the  oscillation.     The  difference  between  the  amplitude  of  two 
successive  oscillations  is  called  the  damping  and  is  a  measure  of  the 
losses.    The  interval  in  time  between  two  successive  oscillations  is  called 
the  period. 

56.  Since  every  body  has  electric  capacity  in  proportion  to  its  surface 
(art.  44),  and  since  movements  of  electric  charges,  without  which  a  body 
can  not  be  electrified,  always  produce  magnetic  fields,  every  body  must 
have  self-induction,  and  therefore  electro-magnetic  oscillations  can  take 
place  in  it. 

We  know  that  every  body  vibrates  in  its  own  period  mechanically, 
and  we  find  that  every  body  vibrates  in  its  own  period  electrically,  and 
further  that  the  number  of  vibrations  or  oscillations  per  second  depends 
entirely  on  the  capacity  and  self-induction  of  the  body. 

It  will  be  seen  that  while  a  closed  circuit  is  necessary  for  the  flow  of 
a  continuous  or  direct  current,  for  oscillating  currents  a  straight  wire 
is  sufficient.  A  circuit  containing  a  condenser  which  would  completely 
obstruct  a  direct  current  has  no  effect  on  an  alternating  current  other 
than  to  change  its  sign. 

57.  We  must  be  careful  to  distinguish  between  the  capacity  of  a  con- 
denser and  the  total  charge  in  it,  and  between  the   self-induction  of 
a  wire  and  the  total  induction  caused  by  the  current  in  it.    The  capacity, 
it  may  be  repeated  again,  depends  on  the  material  and  arrangement  of 
the  charged  body.    The  total  charge — that  is,  the  total  electric  induction 
— depends  on  the  capacity  and  the  potential.     In  like  manner  the  self- 
induction  depends  on  the  arrangement  of  the  conductor  and  the  sur- 
rounding material  (whether  iron  or  air).    The  total  magnetic  induction 
depends  on  the  self-induction  and  the  current. 

58.  AVe  can  see  in  a  general  way  that  the  period  of  an  oscillating  circuit 
depends  on  the  capacity  and  self-induction  of  the  circuit,  and  not  on  the 
total  electric  or  total  magnetic  induction,  because  the  capacity  and  self- 
induction  are  determined  by  the  material  and  arrangement  of  the  circuit, 
which  qualities  determine  the  mechanical  period  of  a  body.     It  takes 
longer  to   discharge  a  condenser  of  large  capacity  than  one  of  small 
capacity,  and  it  takes  longer  to  create  a  given  current  in  a  circuit  of 
large  than  in  one  of  small  self-induction.    Increasing  the  potential  gives^ 


42 


MANUAL   OF    WIRELESS    TELEGRAPHY. 


more  work  to  be  done  during  a  discharge,  but  also  gives  power  to  do  it 
in  the  same  ratio,  so  that  increase  of  potential  does  not  change  the  period, 
though  it  may  change  the  amplitude  of  the  oscillations. 

59.  It  was  stated    (art.   29)    that  coiling  a  wire  increases  its  self- 
induction  and  enables  a  strong  magnetic  field  to  be  created  around  it, 
and  that  this  increases  the  electrical  length  of  the  wire — i.  e.,  it  takes  an 
electrical  disturbance  started  at  one  end  of  it  longer  to  reach  the  other 
end  when  the  wire  is  coiled  than  when  the  same  wire  is  straight. 

Now  we  see  that  the  electrical  length  of  a  wire  depends  on  its  capacity 
and  self-induction  and  that  its  period  in  seconds — i.  e.,  the  time  of  one 
complete  oscillation  (the  time  required  for  an  electrical  impulse  started 
at  one  end  to  reach  the  other  and  be  reflected  back) — must  be  twice  its 
electrical  length  divided  by  the  distance  electricity  travels  in  a  second, 
which  we  know  to  be  the  same  as  light  (300,000,000  meters). 

The  capacity  and  inductance  of  a  straight  wire  long  in  proportion  to 
its  thickness  are  so  related  that  its  electrical  length  is  equal  to  its 
natural  length. 

Fr.om  the  above  the  period  or  time  of  one  complete  electrical  oscilla- 
tion of  a  straight  wire  one  meter  long  is  ^J-^^-Q-Q-^-^  second,  and  it 
therefore  oscillates  150,000,000  times  per  second. 

'  The  number  of  oscillations  or  cycles  made  by  an  alternating  current 
per  second  is  called  its  frequency. 

60.  We  know  that  by  coiling  a  wire  its  self-induction  can  be  greatly 
increased,  and  its  period  thereby  lengthened.    By  adding  capacity  to  the 
wire  in  the  shape  of  condensers  its  period  can  be  lengthened  still  more, 
so   that  by   suitable   arrangements  a  circuit   having   small   mechanical 
length,  but  comparatively  great  electrical  length,  can  be  made  up  in  a 
small  space.* 


cx 
o 
o 
o 


FIG.  26. 


FIG.  2  6 A. 


Such  a  circuit  is  shown  in  fig.  26.  It  is  made  up  of  a  condenser  con- 
nected to  a  coiled  wire,  and  will  be  called  in-  this  book  an  oscillating 
circuit. 

*  It  must  not  be  forgotten  that  every  wire  possesses  capacity  by  virtue  of 
its  surface,  and  self-induction  by  virtue  of  the  fact  that  an  electric  current 
can  flow  in  it.  Even  condensers  have  a  certain  amount  of  self-induction. 


MANUAL   OF   WIRELESS   TELEGRAPHY.  43 

The  oscillating  circuit  in  fig.  26  may  have  a  break  or  gap  in  it,  as  in 
fig.  26a,  Tf  the  potential  of  the  condenser  is  sufficient  to  rupture  the 
air  or  other  dielectric  in  the  gap,  the  circuit  does  not  lose  its  oscillating 
character.  The  presence  of  the  gap  does,  however,  decrease  the  number 
of  oscillations  for  one  charge  and  prevents  the  complete  discharge  of  the 
condenser,  because  the  oscillations  cease  as  soon  as  the  potential  falls 
below  a  certain  value.  The  greater  the  loss  or  damping  in  each  oscilla- 
tion the  smaller  the  number  of  oscillations  that  will  take  place  before 
the  potential  falls  so  low  that  the  spark  ceases. 

61.  As  stated  in  art.  48,  the  term  condenser  is  not  satisfactory,  and 
the  word  capacity  is  often  used  to  mean  condenser,  especially  in  con- 
nection with  such  an  oscillating  circuit,  the  condenser  being  spoken  of  as 
a  capacity  and  the  coiled  wire  as  an  inductance,  which  means  a  con- 
ducting wire  arranged  so  as  to  have  large  self-induction. 


-A 


FIG.  27.  FIG.  27A. 

FIG.  27.  —  Inductive  Resistance. 
FIG.  27A.  —  Noninductive  Resistance. 

Fig.  27  represents  an  inductive  resistance,  or  simply  an  inductance, 
since  it  is  assumed  that  all  wires  have  resistance. 

Fig.  27a  represents  a  ncninductive  resistance,  or  simply  a  resistance  — 
it  represents  a  coil  so  wound  that  the  currents  in  adjacent  turns  are  in 
opposite  directions  and  the  coil  has  therefore  no  self-induction. 

62.  An  oscillating  circuit  whose  electrical  length  can  be  varied  at  will 
is  represented  in  fig.  28.  It  consists  of  a  variable  condenser  in  connection 
with  a  fixed  inductance  (fig.  28),  or  it  may  consist  of  a  fixed  condenser 
and  a  variable  inductance  (fig.  28a),  or  both  capacity  and  inductance 


FIG.  28.  FIG.  2 8 A. 

may  be  variable,  the  arrow  in  fig.  28a  being  meant  to  show  that  any 
number  of  turns  of  the  coil  can  be  included  at  will. 

63.  Two  circuits  having  the  same  electrical  length  are  said  to  oscillate 
in  resonance;  their  periods  are  equal,  though  the  inductance  and  capa- 
city may  not  be  the  same  in  each. 
4 


44 


MANUAL    OF    WIRELESS    TELEGRAPHY. 


For  instance,  suppose  the  oscillating  circuit  (28a)  is  adjacent  to  a 
wire,  as  in  fig.  28b,  having  the  same  electrical  length,  we  know  that  for 
oscillating  currents  (see  art.  56)  a  closed  circuit  is  not  necessary.  We 
also  know  that  by  reason  of  their  mutual  induction  (art.  15)  the  closed 
oscillating  circuit,  which  we  can  call  A  B,  will  induce  currents  in  the 
wire,  which  we  can  call  C  D.  Since  their  periods  are  equal  the  induced 
oscillating  current  in  C  D  will  be  suitably  timed  to  the  natural  period  of 
C  D  and  the  two  circuits  will  oscillate  in  resonance.  C  D  can  be  called 
the  open  circuit  as  distinguished  from  A  B,  the  closed  circuit. 


GROUND 

FIG.  28B. 

Oscillating  circuits  now  used  in  wireless  telegraphy  have  electrical 
lengths  varying  from  100  to  5000  meters,  giving  from  1,500,000  to 
30,000  oscillations  per  second.  Those  first  used  by  Marconi  had  electrical 
lengths  of  about  6  centimeters  and  oscillated  approximately  2,500,000,000 
times  per  second. 

ETHER  WAVES. 

64.  As  stated  in  art.  55,  a  cycle  is  made  up  of  two  alternations  or 
movements  in  opposite  directions  and  is  represented  in  fig.  18.  Such 
a  curve  also  represents  the  crest,  hollow,  and  slope  of  regular  waves  on 
the  surface  of  the  ocean  or  other  body  of  water.  The  distance  from  crest 
to  crest  or  from  hollow  to  hollow  of  a  water  wave  is  called  a  wave  length, 
and  this  distance  is  equal  to  that  of  two  alternations.  Since  electro- 
magnetic (ether)  disturbances  spread  in  all  directions  with  the  speed  of 
light,  and  when  sent  out  by  an  oscillating  current  succeed  each  other  at 
equal  intervals  of  time,  and  since  the  magnetic  and  electric  forces  pro- 
duced by  oscillating  currents  change  direction  during  each  alternation, 
just  as  the  particles  of  water  rise  to  the  crest  or  fall  to  the  hollow  of  a 
wave,  their  positive  and  negative  amplitudes  may  represent  the  crests  and 


MANUAL   OF   WIRELESS    TELEGRAPHY.  45 

hollows  of  waves  separated  by  half  periods  or  half  wave  lengths,  an 
oscillating  current  may  be  called  a  wave  producer,  and  the  oscillations 
considered  as  movements  of  the  ether  may  be  called  ether  waves. 

65.  Hertz  (in  1886  at  Carlsruhe,  Germany)  was  the  first  to  show  that 
oscillating  electric  currents  really  do  produce  ether  waves — like  those  of 
light  only  longer  and  subject  to  all  the  laws  governing  light  waves.    For 
this  reason,  wireless  is  sometimes  called  Hertzian  wave  telegraphy. 

66.  The  vibrations  of  particles  producing  sound  waves,  as  in  air,  con- 
sists of  to-and-fro  movements  parallel  to  the  direction  of  the  waves,  the 
latter  consisting  of  alternating  conditions  of  compression  and  rarefaction 
of  the  air. 


FIG.  18. 

The  movement  of  the  particles  in  ether  waves  is  at  right  angles  to 
the  direction  of  propagation  of  the  wave,  and  the  electric  and  magnetic 
movements  are  also  at  right  angles  to  each  other  at  any  point  in  the 
wave  front.  This  is  called  transversal  vibration,  as  distinguished  from 
the  longitudinal  vibration  of  the  particles  in  sound  waves. 

When  one  particle  'of  a  substance  is  displaced  or  made  to  vibrate,  it 
induces  its  neighbors  to  follow  it,  and  starts  them  to  vibrating  in  the 
same  periods  but  in  different  phases,  each  particle  starting  to  vibrate 
(passing  the  word,  so  to  speak)  at  a  definite  interval  of  time  after  the 
one  next  to  it  has  started.  The  vibrations  may  be  longitudinal  or  trans- 
verse, as  described  above,  or  they  may  be  circular  or  elliptical,  but  if  they 
are  regular  the  waves  produced  are  regular. 

The  amplitude  of  the  wave  (art.  55)  depends  on  the  extreme  limits 
from  its  normal  position  of  the  vibration  of  each  individual  particle. 
The  wave  length  depends  on  the  time  of  one  complete  vibration  of  each 
particle  and  the  velocity  with  which  the  displacement  or  vibration  is 
propagated  from  one  particle  to  another  of  the  substance.  It  is  found 
that  this  velocity  is  equal  to  the  square  root  of  the  elasticity  of  the  body 
divided  by  its  density. 


46  MANUAL    OF    WIRELESS    TELEGRAPHY. 

We  know  that  this  velocity  in  the  ether  is  300,000,000  meters  per 
second,  and  we  conclude  that  the  ether  must  have  very  great  elasticity 
combined  with  very  small  density. 

It  has  been  stated  that  electric  charges  or  electrons  are  the  only  things 
which  have  a  grip  on  the  ether,  and  that  when  they  are  vibrating  the 
ether  vibrates  with  them. 

When  a  particle  is  subject  to  several  forces  at  the  same  time,  its 
resultant  movement  depends  on  the  resultant  of  the  forces  and  will  vary 
as  the  forces  vary,  so  that  a  body  can,  in  effect,  vibrate  in  more  than  one 
way  at  the  same  time,  and  can  produce  complex  waves  where  vibrations 
are  superimposed  on  each  other.  This  is  shown  every  day  at  sea  by  the 
small  waves  or  ripples  on  the  slopes  of  large  ones,  or  the  short  waves  from 
local  winds  superimposed  and  propagated  in  the  same  or  different 
directions  from  the  long  swells  due  to  distant  storms. 

67.  The  vibrations  producing  ether  waves,  and  consequently  the  wave 
lengths  and  frequencies,  are  of  an  almost  infinite  range,  for  instance: 

Ether  vibrations  from  430  to  740  trillions  per  second  (a  little  less 
than  one  octave)  are  visible  to  the  eye  and  are  called  light. 

Between  870  to  1500  trillions  of  vibrations  per  second  we  have  the 
ultraviolet  and  X-rays,  and  from  430  down  to  300  trillions  of  vibrations 
per  second  what  are  called  infrarouge  rays. 

Below  300  and  down  to  20  trillions  of  vibrations  per  second  we  detect 
ether  vibrations  by  our  sense  of  feeling  or  by  the  thermometer,  and  they 
are  called  heat. 

Forty-five  octaves  lower  on  the  same  scale  are  the  ether  vibrations 
which  we  call  electric  waves  and  which  are  used  in  wireless  telegraphy. 
The  shortest  of  these  yet  measured  is  0.2  of  an  inch  in  length;  the 
longest,  over  1,000,000  miles. 

Marconi,  in  his  first  experiments,  used  a  pair  of  small  spark  balls 
which  gave  out  waves  about  12  centimeters  in  length. 

68.  Ether  waves  of  all  lengths   are  subject  to  reflection,  refraction, 
diffraction,   and  absorption,  and  bodies,   such   as  insulators  of  certain 
kinds,  which  are  opaque  to  the  short  waves  we  call  light,  are  transparent 
to  the  long  electric  waves  used  in  wireless  telegraphy.     Practically  all 
conductors  are  opaque  to  electric  waves.     Generally  speaking,  insulators 
are  transparent  to  electric  waves,  but  in  transmitting  the  wave  they 
absorb  some  of  its  energy. 

Conductors,  being  opaque  to  electric  waves,  partially  reflect  and  par- 
tially absorb  the  wave  energy. 

A  simple  case  of  wave  reflection  is  seen  when  a  rope  hanging  vertically 
is  given  a  quick  jerk  and  then  held  taut  in  the  hand.  A  wave  can  be 
seen  traveling  up  the  rope  till  it  reaches  the  top,  where  it  is  reflected, 
travels  down  the  rope  to  the  hand,  is  reflected  there  and  starts  up  again 
to  the  top,  and  so  continues  until  its  energy  is  damped  out. 


MANUAL    OF    WIRELESS    TELEGRAPHY. 


47 


If  a  number  of  equally  timed  jerks  are  given,  a  succession  of  waves 
at  equal  intervals  is  sent  up  the  rope.  When  reflected  back  they  meet 
others  coming  up  whose  lengths  are  equal  to  those  coming  down.  At 
some  points  the  rope  tends  to  move  a  certain  distance  in  one  direction 
with  the  direct  wave,  and  the  same  distance  in  the  opposite  direction 
with  the  reflected  wave;  the  result  is  that  it  does  not  move  at  all. 
These  points  are  found  along  the  rope  one-half  wave  length  apart;  at 
all  other  points  the  rope  moves  or  vibrates  in  the  resultant  direction 
of  the  direct  and  reflected  wave  impulse,  and  what  are  called  stationary 
waves  are  set  up. 

The  points  at  which  there  is  no  movement  are  called  nodes,  and  points 
at  which  there  is  maximum  movement  are  called  loops.  This  is  shown 
graphically  in  fig.  18c. 


FIG.  18c. 

Stationary  ether  waves  can  be  set  up  around  conducting  wires  by  suit- 
ably timed  electrical  impulses  applied  to  the  ends  of  the  wires. 

69.  It  will  be  observed  that  the  point  of  support  of  the  rope  where  it 
can  not  move  must,  in  every  case,  be  a  node.  So  in  a  conducting  wire, 
the  end  of  the  wire  away  from  that  receiving  the  impulses  must  be  a 
current  node,  because  no  current  can  flow  there.  It  can,  however,  and  a 
little  consideration  will  show  that  it  must,  be  a  potential  loop,  for  while 
there  is  no  movement  at  the  point  of  support,  the  greatest  pressure  or 
tendency  to  move  is  there. 

Since  the  electrical  impulses  consist  of  variations  of  current  and 
potential,  which  succeed  each  other  regularly,  and  since  at  a  given  point 
we  find  a  loop  of  potential  and  a  node  of  current,  we  must,  at  a  quarter- 
wave  length  distant,  find  a  node  of  potential  and  a  loop  of  current. 

This  is  shown  graphically  in  fig.  18d,  which  represents  the  relative 
positions  of  current  and  potential  nodes  and  loops  in  stationary  electric 


POTENTIAL  LOOP 
CURRENT  Nooe 


FIG.  18D. 


48  MANUAL   OF   WIRELESS   TELEGRAPHY. 

waves,  and  illustrates  the  statements  made  in  art.  54  (figs.  25a,  etc.), 
relative  to  the  alternations  of  electric  and  magnetic  fields  in  oscillating 
condenser  discharges. 

70.  If  an  oscillating  current  be  set  up  in  a  free  wire  (fig.  18e)  by  a 
neighboring  discharging  circuit  in  resonance  with  it,  the  free  wire  will 
be  found  by  measurement  with  a  micrometer  spark  gap  to  have  an  alter- 
nating potential  in  it,  varying  from  nothing  at  the  middle  point,  C,  to  a 
maximum  at  either  end  somewhat  similar  to  the  full  curve  EOF. 


B 


PIG.  18E. 

If  at  the  same  time  the  current  in  the  free  wire  could  be  measured,  it 
would  be  found  to  have  a  maximum  value  at  C  and  a  minimum  at  the 
ends  similar  to  the  dotted  curve  A  D  B.  If  the  wire  A  C  B  is  not  too 
far  from  the  discharging  resonant  circuit  and  the  wire  be  cut  at  C  and 
an  incandescent  lamp  L  be  connected  to  the  two  halves  as  shown  in  the 
figure,  the  lamp  will  glow. 

REFLECTION  OF  ETHER  WAVES. 

71.  If  ether  waves  impinge  on  a  reflecting  surface  not  normal  to  their 
direction,  they  are  reflected  at  an  angle  equal  to  that  which  the  reflecting 
surface  makes  with  their  original  direction  (the  angle  of  incidence  is 
equal  to  the  angle  of  reflection),  so  that  directed  waves  may  be  detected 
at  points  not  in  the  line  of  direction  by  the  interposition  of  a  reflector. 

Air  at  atmospheric  pressure  (about  760  millimeters  of  mercury)  is 
an  insulator.  Its  density  decreases  with  distance  above  the  earth's  sur- 
face, and  its  insulating  qualities  decrease  with  the  decrease  of  density. 
At  a  height  of  approximately  45  miles  above  the  earth's  surface  its  pres- 
sure is  about  1  millimeter  of  mercury.  At  the  density  corresponding  to 
this  pressure  it  is  a  good  conductor,  and  though  still  transparent  to  short 
ether  waves  like  those  of  light,  it  partly  reflects  and  partly  absorbs  long 
ether  waves.  In  the  intermediate  distance  it  is  at  first  transparent,  then 
partially  transparent,  absorbent,  and  reflecting,  simultaneously. 

It  is  known  that  ether  waves  are  guided  by  conducting  surfaces  to  a 
certain  extent  (for  instance,  by  wires),  as  well  as  reflected  by  them,  and 
that  otherwise  they  travel  in  straight  lines.  Fig.  18f  shows  the  approxi- 
mate path  of  an  ether  wave  started  from  the  earth's  surface  and  reflected 


MANUAL    OF   WIRELESS    TELEGRAPHY.  49 

from  the  upper  atmosphere.  It  will  be  seen  that  even  if  the  earth's 
surface  did  not  guide  the  waves  they  might  be  detected  at  points  below 
the  horizon. 

Other  causes  of  reflection  may  exist.,  such  as  large  bodies  of  electrified 
air,  or  heavily  charged  clouds,  which  would  cause  interference  between 
direct  and  reflected  waves  and  make  electrical  shadows  at  certain  places, 
i.  e.,  points  at  which,  owing  to  conditions  outlined  above,  either  the 
waves  are  so  attenuated  that  they  can  not  be  detected  or  they  are  com- 
pletely neutralized. 


FIG.  18F. 
REFRACTION  OF  ETHER  WAVES. 

72.  When  ether  waves  impinge  on  transparent  bodies  at  any  angle 
other  than  the  normal,  if  their  velocity  in  the  transparent  body,  on 
account  of  its  elasticity  or  density,  is  different  from  that  at  which  they 
were  previously  moving,  that  part  of  the  wave  first  entering  the  body 
will  move  either  faster  or  slower  than  it  did  before.     The  part  outside 
will  therefore  either  fall  behind  or  gain  on  the  first  part.    This  action  will 
affect  each  portion  of  the  wave  front  as  it  enters  the  body,  and  the  result 
will  be  that  its  direction  of  movement  will  be  changed.    The  effect  is  to 
bend  the  wave  out  of  its  original  path,  and  the  action  is  called  refraction. 

Ether  waves  passing  through  the  atmosphere,  whose  density  varies  at 
different  points,  are  subject  to  this  bending  action. 

DIFFRACTION  OF  ETHER  WAVES. 

73.  When  waves  meet  a  body  in  their  path   (for  instance,  when  the 
comparatively  long  waves  used  in  wireless  telegraphy  impinge  on  a  high 
island  or  mountain  range)    at  the  points  where  the  wave  front  cuts 
the  extreme  width  of  the  island  and  along  the  crest  or  summit  new  cen- 
ters of  disturbance  are  created,  which  radiate  some  of  the  wave  energy  to 
points  behind  the  island.    It  has  the  effect  of  bending  the  waves  around 
the  object,     This  action  of  waves  is  called  diffraction.     In  amount  it 
depends  on  the  wave  length.    From  the  new  centers  of  disturbance  waves 
are  sent  out,  which  interfere  with  each  other,  not  being  propagated  in 
the  same  directions.    The  result  is  that  for  a  distance,  depending  on  the 


50 


MANUAL    OF    WIRELESS    TELEGRAPHY. 


width  and  height  of  the  obstacle  and  on  the  wave  length,  a  shadow  exists 
beyond  it. 

Partial  reflection  of  the  waves  toward  their  source  takes  place  on  the 
side  of  the  obstacle  nearest  the  source.  An  attempt  to  show  this  graphi- 
cally is  made  in  fig.  18g,  but  the  best  illustration  is  given  by  the  motion 
of  water  around  a  rock  on  a  windy  day.  The  small  back  waves  on  the 
windward  side  are  reflected  to  windward.  The  waves  circling  or  bend- 
ing around  the  rock  are  diffracted.  The  still  water  in  the  lee  of  the  rock 
is  the  shadow,  in  which  no  action  exists.  At  a  distance  depending  on 
the  size  of  the  rock  and  the  wave  length  the  zones  of  interference  disap- 


FIG.  18a. 

pear,  the  regular  waves  from  the  two  sides  of  the  rock  unite,  and  there 
is  no  evidence  of  its  existence  at  points  beyond,  though  it  has  decreased 
the  total  strength  of  the  waves. 

For  the  above  reasons  high  land  between  two  wireless  telegraph 
stations  has  the  effect  of  decreasing  the  strength  of  signals  at  each 
station,  and  if  close  to  either  station  may  entirely  prevent  that  station 
from  receiving.  (It  may  be  in  the  shadow  or  be  subject  to  interference 
from  reflection.) 

The  effects  of  reflection  and  diffraction  on  waves  passing  over  irregular 
country  are  very  pronounced.  The  effects  of  reflection,  refraction,  and 
absorption  in  the  atmosphere  are  equally  pronounced,  the  qualities  of  the 
atmosphere  in  all  three  respects  varying  greatly  from  day  to  day  and 
between  day  and  night. 

An  ether  wave  traveling  from  one  wireless-telegraph  station  to  another 


MANUAL    OF    WIRELESS    TELEGRAPHY. 


51 


over  rough  country  and  through  an  atmosphere  of  varying  density,  work- 
ing its  way  around  and  over  mountains,  being  balloted  from  thunder 
clouds  at  one  point  and  absorbed  by  semiconducting  gases  at  another, 
may  be  said  to  pursue  an  adventurous  journey. 

PRODUCTION    OF   ETHER    WAVES. 

74.  We  have  now  seen  how  to  produce  electric  and  magnetic  fields, 
how  to  utilize  magnetic  fields  for  the  production  of  electric  currents  in 
dynamos,  how  to  increase  the  potential  of  these  currents  by  means  of 
step-up  transformers,  and  ho\v  by  means  of  this  high  potential  current 
to  force  large  charges  into  electric  accumulators  or  condensers  and  by 
discharging  these  condensers  in  oscillating  circuits  to  produce  what  we 
call  electric  or  ether  waves.  These  operations  can  be  represented  graphi- 
cally or  diagrammatically,  as  in  fig.  29,  which  shows  a  separately  excited 
A.  C.  dynamo  in  circuit  with  the  primary  winding  of  a  step-up  trans- 
former, whose  secondary  charges  the  condenser  of  an  oscillating  circuit 
containing  a  spark  gap. 


GROUND 


FIG.  29. 


The  secondary  winding  of  the  transformer  is  of  many  turns,  in  order 
to  give  a  high  potential.  The  transformer  also  has  an  iron  core.  The 
great  number  of  turns  of  the  secondary  winding,  added  to  the  effect 
produced  by  the  iron  core,  gives  the  circuit  containing  the  secondary 
winding  and  the  condenser  a  very  large  self-induction,  and  consequently 
a  very  long  period.  The  circuit  composed  of  the  condenser,  self-induc- 
tion, and  spark  gap  has  a  very  much  shorter  period,  and  when  the  spark 
gap  is  ruptured  this  circuit  oscillates  as  if  it  were  entirely  disconnected 
from  the  secondary,  usually  completing  its  oscillations  and  coming  to  rest 
in  a  fraction  of  the  period  of  the  circuit  formed  by  the  secondary  winding 
and  condenser. 


MANUAL    OF    WIRELESS    TELEGRAPHY. 


The  oscillating  circuit  (condenser,  spark  gap,  and  inductance)  is 
shown  in  fig.  29  near  a  conducting  wire,  having 
a  few  turns  of  inductance  close  to  those  of  the 
oscillating  circuit.  In  this  circuit  we  can  con- 
sider the  condenser  as  representing  the  source  of 
current,  like  the  hattery  in  fig.  11,  art.  12;  the 
spark  gap  as  the  break  K,  the  turns  of  inductance 
in  the  oscillating  circuit  as  A  B,  and  the  open 
circuit  with  one  end  grounded  as  C  D.  The 
oscillating  currents  in  A  B  produce  like  cur- 
rents, but  in  the  opposite  direction  in  C  D  (art. 
FIG.  11.  12),  and  C  D  becomes  a  source  of  ether  waves. 

75.  The  production  of  ether  waves  and  their  detection  at  a  distance 
from  the  source  constitutes  wireless  telegraphy. 

C  D  is  usually  called  the  open  or  radiating  circuit. 
A  B  the  closed  or  oscillating  circuit. 

The  two  inductances  in  A  B  and  C  D  form  the  primary  and  secondary, 
respectively,   of  an  air-core  oscillation  transformer    (art.   27).     When 
arranged  as  in  fig.  29,  A  B  and  C  D  are  said  to  be  inductively  connected. 
C  D  may  have  part  of  its  inductance  common  to  A  B.    The  arrange- 
ment in  this  case  acts  as  an  auto-trans- 
former, and  the  circuits  are  said  to  be 
direct  connected  (fig.  29a). 

If  the  oscillating  and  radiating  cir- 
cuits have  the  same  period,  they  oscillate 

C      °  O(^  or  vibrate  in  resonance.     The  radiating 

J     <f  £^          circuit  in  such  a  case  receives  ^the  in- 

ductive impulses  from  the  oscillating 
circuit  at  the  proper  time,  and  the  am- 
plitude of  its  oscillations  is  thereby  in- 
creased. 

The  adjustment  of  A  B  and  C  D  to 

any  given  period  and  their  adjustment  to  each  other's  periods  is  called 
tuning. 

It  will  be  noted  that  the  oscillating  circuit  has  concentrated  capacity, 
while  the  capacity  of  the  radiating  circuit  is  distributed. 

76.  The  fundamental  principle  of  wireless  telegraphy  is  that  all  bodies 
viorate  electrically  as  well  as  mechanically ;  that  their  periods  of  electrical 
vibration  depend  solely  on  the  capacity  and  self-induction  of  the  vibrat- 
ing body;  that  these  electrical  vibrations  produce  ether  waves  which  are 
propagated  with  the  speed  of  light,  and  which  can  be  detected  at  great 
distances  from  their  source  by  means  of  instruments  specially  designed 
for  the  purpose. 


SLABY  ARCO 


TO  AWIAU 


T 


FIG.  29A. 


Chapter  II. 

QUANTITATIVE  CONSIDEBATION  OF  HIGH  FREQUENCY 

PHENOMENA. 

UNITS. 

77.  Attention  has  thus  far  been  concentrated  on  the  quality  rather 
than  the  quantity  of  the  electro-magnetic  actions  under  discussion.    Be- 
fore proceeding  further  it  is  necessary  to  consider  the  standards  of 
measurement  adopted  and  their  relation  to  each  other. 

78.  Electric  and  magnetic  actions  being  forms  of  energy,  and  being 
mutually  convertible,  as  we  have  seen,  are  subject  to  all  the  laws  govern- 
ing transformations  of  energy. 

Work  is  done  when  conductors  are  moved  in  magnetic  fields,  the  re- 
sistance to  movement  and  the  amount  of  movement  determining  the 
amount  of  work  done. 

The  unit  of  mechanical  work  is  a  foot-pound,  by  which  name  we 
designate  the  work  done  in  lifting  1  pound  1  foot  against  the  action  or 
force  of  gravity. 

Force,  by  which  we  mean  the  cause  of  action  or  movement  (pulling  or 
pushing  ability),  is  measured  in  pounds,  and  force  multiplied  by  the 
distance  through  which  it  acts  is  work.  Lifting  10  pounds  10  feet  =100 
foot-pounds. 

The  amount  of  work  done  in  a  given  time — that  is,  the  rate  of  doing 
work — is  called  power.  The  unit  of  mechanical  power  we  call  a  horse- 
power, and  it  represents  a  rate  of  doing  work  equal  to  33,000  foot-pounds 
per  minute,  or  550  foot-pounds  per  second. 

In.  the  above  definitions  of  work  and  power  the  units  of  distance, 
weight  (or  mass),  and  time  used  are  the  foot,  pound,  and  minute,  all  of 
which  are  defined  by  law  and  are  called  fundamental  units. 

79.  Another  system  of  units,  proposed  by  the  British  Association  for 
the    Advancement    of    Science    and    now   generally    used    in   electrical 
measurements,   is  based  on  the  centimeter,  gram,  and  second,  and  is 
usually  called  the  c.  g.  s.  system.     The  use  of  this  system  is  authorized 
by  law  and  is  universal  in  scientific  work. 

The  following  relations  exist  between  the  two  sets  of  units : 
1  foot      =   30.48  centimeters,  approximately. 
1  pound  =453.59  grams,  approximately. 
1  minute  •=   60        seconds.* 

*  The  unit  of  time  is  based  on  a  fundamental  unit,  being  a  fraction  of  the 


54  MANUAL    OF    WIRELESS    TELEGRAPHY. 

The  units  of  length  and  weight  in  the  United  States  are  kept  at  the 
Bureau  of  Standards  in  Washington,  and  the  unit  of  time  is  determined 
by  the  Naval  Observatory  in  the  same  city. 

The  unit  ofjorce  in  the  c.  g.  s.  system  is  that  force  which,  acting  on  a 
gram  mass  for  1  second  gives  it  a  velocity  of  1  centimeter  per  second. 
This  force  is  called  a  dyne. 

The  force  of  gravity  acting  on  a  gram  mass  for  1  second  will  give  it 
a  velocity  of  32.2  feet  per  second  =  approximately  981  centimeters  per 
second;  therefore  the  force  of  gravity  is  equal  to  981  dynes  and  the  pull 
of  a  dyne  represented  as  a  weight  is  equal  to  g~|-T  of  a  gram. 

The  pull  of  a  pound,  which  equals  453.59  grams,  must  be  equal  to  that 
of  453.59x981  =  approximately  445,000  dynes. 

The  unit  of  work  in  the  c.  g.  s.  system  is  the  work  done  in  overcoming 
the  force  of  1  dyne  through  1  centimeter,  and  is  called  an  erg.  In  other 
words,  an  erg  is  the  work  done  in  lifting  ¥-J-T  of  a  gram  1  centimeter. 

An  erg  by  definition  is  a  dyne  overcome  through  a  centimeter,  and  we 
see  that  a  foot-pound  is  445,000  dynes  overcome  through  30.48  centi- 
meters; therefore  a  foot-pound  equals  445,000x30.48  =  approximately 
13,570,000  ergs,  and  a  horse-power,  which  equals  550  foot-pounds, 
per  second  =  13,570,000x550  =  approximately  7,460,000,000  ergs  per 
second. 

.  80.  The  c.  g.  s.  units  of  distance  (centimeter),  time  (second),  force 
(dyne),  and  work  (erg)  are  employed  to  define  the  absolute  units  used 
in  electrical  measurements.  These  are  electro-motive  force,  current, 
and  resistance.  (Art.  3,  art.  26.)  From  these  are  derived  the  so-called 
practical  units  in  daily  use — volt,  ampere,  or  ohm. 

On  account  of  the  fact  that  the  names  adopted  for  the  practical  electro- 
magnetic units  are  all  names  of  noted  scientists  and  not  related  to  nor 
in  any  way  descriptive  of  the  qualities  they  are  used  to  designate,  their 
acquirement  must  be  entirely  a  feat  of  memory.  They  can  be  more  easily 
remembered  by  associating  them  with  the  names  of  the  theoretical  or 
absolute  units. 

By  agreement  among  electricians,  electro-motive  force  is  represented 
by  the  letter  E;  electric  current  by  the  letter  I;  resistance  to  the  flow  of 
electricity  by  the  letter  E;  time  by  the  letter  T;  work  by  the  letter  W; 
power  by  the  letter  P. 

81.  We  know  that  it  requires  work  to  move  conductors  in  magnetic 
fields,  or  one  magnet  in  the  vicinity  of  another,  and  the  movement 
generates  an  E.  M.  F.  in  the  conductor. 

time  of  a  revolution  of  the  earth,  and  this  unit  is  common  to  both  systems. 
The  foot  and  the  pound  are  really  arbitrary  units.  The  centimeter  is  a 
fraction  of  a  fundamental  unit,  namely,  of  the  distance  from  the  equator  to 
the  north  pole  on  a  certain  meridian.  The  gram  is  the  weight  of  a  cubic 
centimeter  of  distilled  water.  It  is  an  arbitrary  unit. 


MANUAL    OF    WIRELESS    TELEGRAPHY. 


55 


Magnetic  fields  are  represented  in  strength  by  the  number  of  lines  of 
force  per  square  centimeter  that  they  contain. 

Unit  magnetic  field  is  said  to  contain  one  line  of  force  per  square 
centimeter  (the  field,  of  course,  being  uniform  throughout),  and  is  such 
a  field  as  will  act  on  unit  magnetic  pole  with  a  force  of  1  dyne.  Unit 
pole  being  such  a  pole  as  will,  when  placed  a  distance  of  1  centimeter 
in  air  from  a  similar  pole  of  equal  strength,  be  repelled  by  a  force  of  1 
dyne. 

Moving  a  conductor  across  unit  field  so  that  it  cuts  1  square  centi- 
meter of  the  field  per  second  generates  unit  E.  M.  F. 

If  the  conductor  forms  part  of  a  closed  circuit  and  the  current  gen- 
erated in  it  is  such  that  when  cutting  1  square  centimeter  of  unit  field 
per  second  its  movement  is  opposed  by  a  force  of  1  dyne,  the  circuit  is 
said  to  have  unit  resistance,  unit  current  is  said  to  flow,  and  the  work 
done  is  1  erg  per  second  (the  force  of  a  dyne  overcome  through  a  centi- 
meter) . 

I 


FIG.  15. 

82.  Let  fig.  1 5  represent  unit  magnetic  field  between  two  magnet  poles 
N  and  S.  Let  C  D  represent  a  conductor  one  centimeter  in  length  mov- 
ing at  right  angles  to  this  field  at  the  rate  of  one  centimeter  per  second, 
and  making  sliding  connections  at  its  ends  with  a  very  heavy  conductor 
whose  resistance  as  compared  with  C  D  is  so  small  that  it  can  be  neg- 
lected and  the  resistance  of  the  circuit  considered  as  concentrated  in  C  'D. 

Then,  if  it  requires  a  pull  of  1  dyne  (1/981  gram)  to  keep  C  D  moving 
at  the  rate  of  one  centimeter  per  second,  C  D  has  unit  resistance,  unit 
current  flows,  and,  by  definition,  unit  E.  M.  F.  is  generated. 

If  the  speed  of'C  D  is  doubled,  the  E.  M.  F.  is  doubled  and  the  cur- 
rent (as  shown  by  the  effects)  is  doubled,  we  can  express  this  by  saying: 


56  MANUAL    OF    WIRELESS    TELEGRAPHY. 

(a)  Current  varies  directly  as  E.  M.  F.  If  the  size  of  C  D  is  doubled 
(the  speed  remaining  the  same)  the  resistance  is  reduced  to  one-half, 
but  it  requires  a  pull  of  2  dynes  to  keep  up  the  same  speed,  and  we  find 
that  the  current  is  doubled  as  before;  we  say:  (b)  Current  varies  in- 
versely as  resistance.  Combining  (a)  and  (b)  we  can  say  current 
E.M.P.  _7*(1). 


resistance  R 

Equation  (1)  is  the  fundamental  electrical  equation  and  states  in 
mathematical  form  what  is  known  as  Ohm's  law,  viz. :  "  The  current  in 
any  circuit  varies  directly  as  the  electro-motive  force,  and  inversely  as 
the  resistance  in  the  circuit." 

83.  Doubling  the  current  doubles  the  opposition  to  movement  and, 
other  things  remaining  the  same,  doubles  the  work  per  second,  or  the 
power.    Power,  therefore,  varies  directly  as  the  current. 

Doubling  the  speed  of  movement  doubles  the  electro-motive  force  and 
also  the  current,  but  it  quadruples  the  power  of  work  done  per  second 
since  it  represents  a  pull  of  two  dynes  through  2  centimeters  in  one 
second.  Power,  therefore,  varies  directly  as  the  E.  M.  F.,  as  well  as 
directly  with  the  current,  and  we  can  say  that  it  varies  as  their  product, 
OT  P  =  I  E  (2). 

84.  Since  magnetic  fields  containing  20,000  lines  of  force  per  square 
centimeter  can  be  obtained,  a  rate  of  cutting  of  one  line  per  second 
gives  too  small  a  unit  of  E.  M.  F.  for  practical  use. 

On  the  other  hand,  the  current  necessary  to  produce  a  resistance  of 
1  dyne  to  this  slow  movement  in  unit  field  is  somewhat  large,  therefore 
to  replace  the  theoretical  or  absolute  units  the  so-called  practical  units 
have  been  adopted. 

VOLT. 

The  practical  unit  of  E.  M.  F.  is  the  volt  and  is  the  E.  M.  F.  generated 
when  lines  of  force  are  cut  at  the  rate  of  100,000,000  per  second. 

AMPERE. 

The  practical  unit  of  current  is  the  ampere  and  is  one-tenth  of  the 
theoretical  unit. 

OHM. 

In  order  to  maintain  the  truth  of  the  equation  1=^-  (1)>  the  prac- 
tical unit  of  resistance,  which  is  the  ohm,  is  taken  as  1,000,000,000 
times  the  theoretical  or  absolute  unit. 

Ohm's    law    then    still    remains    true.      I—  -=  or    amperes  =-  ^, 


MANUAL    OF    WIRELESS    TELEGRAPHY.  57 

because  this  equation  in  terms  of  the  absolute  units  is  ^TT  (amperes)  = 
(volts)     wMch  ig  the  game  ag  I=Em     The  size  Qf 


72X1,000,000,000  (ohms)  '  R 

the  units  has  been  changed,  but  the  proportion  between  them  is  the  same 

as  before. 

WATT. 

The  practical  unit  of  power  is  the  watt,  which  is  the  ergs  of  work 
done  per  second  when  1  ampere  is  flowing  with  an  E.  M.  F.  of  1  volt. 
This  in  ergs  (see  equation  (2))  equals  unit  E.  M.  F.x  100,000,000  X 

unit  current^  Qr  10^000^000  ergg  per  second.     Therefore  1  watt  equals 

10,000,000  ergs  per  second.  The  power  expended  in  any  circuit  in  watts 
equals  the  product  of  the  volts  and  amperes  in  the  circuit,  or  P=IE  (2). 

Ten  million  ergs  of  work  is  called  a  joule.  Therefore  a  watt=l  joule 
per  second. 

We  have  seen  that  1  H.  P.  =  7,460,000,000  ergs  per  second.  There- 
fore 1  H.  P.  =  746  watts.  1  watt  =  approximately  0.737  foot-pounds  per 
second. 

85.  After  having  selected  the  practical  units,  it  became  necessary,  for 
the  purpose  of  comparison  and  for  everyday  use,  to  represent  them  in 
practical  form,  because  the  accurate  measurement  of  dynes  and  ergs  is  a 
very  difficult  matter  practically. 

But  it  can  be  done  in  accordance  with  definitions  given  in  art.  78.  Also 
art.  81  indicates  how  to  measure  the  strength  of  magnetic  fields  and  how 
to  determine  and  compare  E.  M.  Fs.  and  currents  by  the  ergs  of  work 
done  in  creating  them.  A  volt  or  an  ampere  can  thus  be  definitely 
created. 

The  current  from  certain  primary  batteries  is  found  to  be  constant 
when  their  terminals  are  connected  by  the  same  wire  : 

Since  current  and  resistance  are  constant,  the  voltage  of  such  cells 
must  be  constant,  and  this  voltage  once  determined  by  comparison  with 
absolute  volts  as  determined  above,  we  have  at  once  a  practical  concrete 
standard  of  E.  M.  F. 

It  is  found  that  the  decomposition  of  an  electrolyte  (art.  1),  by  an 
electric  current,  always  results  in  the  separation  or  deposit  of  exactly 
equal  quantities  of  the  constituents  of  the  electrolyte  for  equal  quantities 
of  current.  The  deposit  in  a  certain  time,  being  weighed,  serves  as  a 
very  accurate  measurement  of  the  amount  of  electricity  which  passes  in 
that  time,  and  consequently  affords  a  very  accurate  means  of  comparing 
electric  currents.  When  1  ampere  determined  as  above  is  passed  through 
a  given  electrolyte,  the  weight  of  material  deposited  gives  us  at  once  a 
practical  standard  of  current. 


58  MANUAL   OF   WIRELESS    TELEGRAPHY. 

XT 

86.  On  account  of  the  relation  7=-=-(l)  between  amperes,  volts,  and 

xt 

ohms  in  a  circuit,  if  any  two  of  them  are  known  the  other  is  also  known, 
so  that  only  two  measurements  of  concrete  units  are  required.  The 
question  of  which  two  should  be  selected  and  the  exact  form  that  each 
should  take  has  been  the  subject  for  discussion  at  a  number  of  inter- 
national conferences,  the  latest  of  which  has  recommended  that  only 
two  electrical  units  shall  be  chosen  as  fundamental  units,  viz.,  the  inter- 
national ohm  defined  by  the  resistance  of  a  column  of  mercury,  and  the 
international  ampere  defined  by  the  deposition  of  silver. 

The  volt  to  be  defined  as  the  E.  M.  F.  which  produces  an  electric  cur- 
rent of  1  ampere  in  a  conductor  whose  resistance  is  1  ohm. 

Different  methods  of  measurements  produce  slight  differences  in  the 
values  of  the  standards,  but  the  values  recognized  by  law  in  the  United 
States  are  as  follows : 

The  standard  (international)  ohm  is  the  resistance  offered  to  an  un- 
varying electric  current  by  a  column  of  mercury  at  the  temperature  of 
melting  ice — 14.4521  grams  in  mass — of  a  constant  cross-sectional  area, 
and  of  a  length  of  106.3  centimeters. 

The  standard  (international)  ampere  is  the  unvarying  current  which, 
when  passed  through  a  solution  of  'nitrate  of  silver  in  water  in  accordance 
with  certain  specifications,  deposits  silver  at  the  rate  of  0.001118  of  a 
gram  per  second. 

As  previously  stated,  a  volt  is  the  E.  M.  F.  which  if  steadily  applied 
to  a  conductor  whose  resistance  is  1  ohm  will  produce  a  current  of  1 
ampere:  but  a  concrete  standard  for  the  volt  is  also  recognized  by  law, 
it  being  specified: 

That  the  electrical  pressure  at  a  temperature  of  15°  centigrade  between 
the  poles  or  electrodes  of  the  voltaic  cell  known  as  Clark's  cell,  prepared 
in  accordance  with  certain  specifications,  may  be  taken  as  not  differing 
from  a  pressure  of  1.434  volts  by  more  than  1  part  in  1000. 

The  latest  international  conference  has  recommended  the  adoption 
of  the  Weston  cadmium  cell  as  preferable  to  the  Clark  for  a  standard 
cell.  The  Weston  cell  has  an  E.  M.  F.  of  1.018  volts  at  20°  C. 

Standard  resistance  wires  having  a  known  ratio  to  the  legal  ohm  are 
made,  and  these,  with  standard  cells,  are  used  for  calibrating  volt  meters 
and  ammeters,  which  are  the  names  given  to  the  galvanometers  for  indi- 
cating automatically  the  E.  M.  F.  and  current  in  any  circuit.  In  this 
way  electrical  values  are  made  uniform  throughout  the  country. 

87.  In  addition  to  the  volt,  the  ampere,  the  ohm,  the  watt,  and  the 
joule  other  practical  units  have  been  adopted,  the  most  important  of 
which,  for  our  purposes,  are : 


MANUAL    OF    WIRELESS    TELEGRAPHY.  59 

COULOMB. 

The  unit  of  quantity,  the  coulomb,  which  is  the  amount  of  electricity 
passing  any  point  in  a  second  when  1  ampere  is  flowing  in  the  circuit. 

FARAD. 

The  unit  of  capacity,  the  farad.  A  condenser  is  said  to  have  a  capacity 
of  1  farad  when  1  coulomb  of  electricity  will  charge  it  to  a  potential 
of  1  volt, 

(Potential  and  E.  M.  F.  are  in  some  senses  identical,  one  being  the 
passive  and  the  other  the  active  state.  An  E.  M.  F.  is  the  result  of 
difference  of  potential.) 

If  this  definition  were  in  terms  of  the  absolute  units,  that  for  capacity 
would  read  : 

A  condenser  is  said  to  have  unit  capacity  when  one  unit  of  electricity 
will  charge  it  to  unit  potential.  Since  by  definition  a  condenser  has 
a  capacity  of  one  farad  when  one-tenth  of  the  absolute  unit  of  elec- 
tricity charges  it  to  a  potential  of  100,000,000,  a  farad  must  equal 

x  =10'9  absolute  imits  of 


HENRY. 

88.  The  unit  of  self-induction,  the  henry.  A  circuit  is  said  to  have  a 
self-induction  of  1  henry  when,  if  the  current  in  it  is  varied  at  the  rate 
of  1  ampere  per  second,  the  induced  E.  M.  F.  —  that  is,  the  counter  or 
reacting  E.  M.  F.  —  tending  to  oppose  the  change  is  1  volt. 

The  definition  of  self-induction  in  terms  of  the  absolute  units  would  be  : 

A  circuit  is  said  to  have  unit  self-induction  when,  if  the  current  in 
it  is  varied  at  the  rate  of  one  unit  per  second,  the  E.  M.  F.  of  self-induc- 
tion is  unity.  Since  by  definition  a  circuit  has  a  self-induction  of  one 
henry;  when,  if  the  current  is  varied  at  the  rate  of  one-tenth  of  unit 
current  per  second,  the  E.  M.  F.  of  self-induction  is  100,000,000,  such 
a  circuit  would  have  an  E.  M.  F.  of  self-induction  10  times  as  great,  or 
1,000,000,000,  if  the  current  instead  of  being  varied  at  the  rate  of  one- 
tenth  unit  per  second  were  varied  at  the  rate  of  one  unit  per  second. 
Therefore  the  unit  of  self-induction,  the  henry,  is.  equal  to  1,000,000,000 
=  109  absolute  units  of  self-induction. 

By  agreement  among  electricians  self-induction  is  represented  by  the 
letter  L;  capacity,  by  the  letter  C. 

*  When  quantities  are  dealt  with  having  a  large  number  of  ciphers  either 
before  or  following  the  significant  figures  it  is  convenient  to  express  them  as 
multiplied  by  some  power  of  ten,  i  e.,  10  =  101,  100  =  102,  T^=  10-1,  Tfo  =  10-*, 
etc. 

5 


60  MANUAL   OF   WIRELESS    TELEGRAPHY. 

Self-induction,  when  expressed  in  terms  of  the  fundamental  units  of 
length,  mass,  and  time,  has  the  dimensions  of  a  length,  and  the  prac- 
tical unit  of  self-induction  was  formerly  called  a  quadrant  on  account 
of  the  fact  that  in  the  metric  system,  an  earth  quadrant — i.  e.,  the  dis- 
tance from  the  equator  to  the  north  pole  =1,000,000,000  centimeters, 
and  since  the  henry  =  1,000,000,000  absolute  units  of  self-inductance,  it 
was  said  to  =  1,000,000,000  centimeters. 

In  this  notation  a  millihenry  =  1,000,000  centimeters.     (See  art.  91.) 

89.  The  units  which  have  been  considered  in  this  chapter  have  been 
derived  from  the  relations  between  electric  currents  and  magnetic  fields 
and  are  called  electro-magnetic  units.     Another  system  of  units,  also 
based  on  the  centimeter,  gram,  and  second,  called  electro-static  units, 
is  in  use.    The  relation  between  the  absolute  units  of  quantity  in  the  two 
systems  is  the  velocity  of  light  in  centimeters  per  second.     This  velocity 
is  30,000,000,000,  or  3xl010  centimeters  per  second,  and  the  electro- 
magnetic unit  of  quantity  =  3  x  1010  electro-static  units. 

The  coulomb,  being  one-tenth  of  the  absolute  unit,  =  3  X 109  electro- 
static units. 

The  electro-magnetic  unit  of  potential  is  -gfa  of  the  electro-static  unit. 

In  both  systems  a  condenser  is  said  to  have  unit  capacity  when  unit 
quantity  of  electricity  charges  it  to  unit  potential. 

From  the  definition  of  a  farad,  given  in  art.  87,  we  see  that  the 
quantity  of  electricity  in  a  condenser  equals  in  coulombs  the  potential 

in  volts  multiplied  by  the  capacity  in  farads,  or  Q  =  EC,  .' .C—  -p- .    Sub- 
stituting for  Q  and  E  their  unit  values   in  electro-static  units  given 

3  X  1 09 
above,  G— j =  9xlOn,  or  the  practical  electro-magnetic,  unit  of 

•JTTO 
capacity  is  9  x  1011  times  as  large  as  the  electro-static  unit. 

The  capacity  of  spherical  bodies  is  found  to  vary  as  their  radii,  and 
in  the  electro-static  system  a  sphere  of  1  centimeter  radius  has  unit 
capacity;  therefore  the  capacity  of  a  sphere  may  be  expressed  by  its 
radius  in  centimeters,  and  capacities  are  still  expressed  by  some  writers 
and  manufacturers  by  the  radius  in  centimeters  of  the  equivalent  sphere. 

A  condenser  having  a  capacity  of  1  farad  has  a  capacity  equal  to  that 
of  a  sphere  having  a  radius  of  9  X 1011  centimeters. 

A  microfarad  (see  art.  91)  =10~6  farads,  is  equal  to  a  capacity  9x 
1011xlO-°  =  9xl05,  or  900,000  centimeters  in  electro-static  units. 

The  earth's  radius  is  approximately  65xlOT  centimeters;  its  capacity 
should  be  approximately  7000  microfarads. 

90.  This  difference  in  units  is  very  confusing,  but  it  exists  particularly 
with  reference  to  the  two  qualities  of  self-induction  and  capacity  with 
which  wireless   telegraphy   is   intimately   concerned.     Microfarads   and 


MANUAL    OF    WIRELESS    TELEGRAPHY.  61 

millihenrys  will  be  used  in  this  book,  and  where  centimeters  are  found 
as  in  some  catalogues  and  some  books  on  electricity,  the  relations  here 
given  —  1  millihenry  =  1,000,000  centimeters  electro-magnetic  units;  1 
microfarad  =  900,000  centimeters  electro-static  units  —  will  enable  one  set 
of  units  to  be  converted  into  the  other. 

The  entire  system  of  units  used  in  electrical  measurements  is  a  monu- 
ment to  the  ingenuity  of  scientists,  but  productive  of  many  difficulties 
to  students. 

91.  While  the  volt,  the  ampere,  and  the  ohm  are  really  practical  units, 
the  farad  and  henry  are  too  large  for  practical  use. 

It  would  take  a  very  large  condenser  to  have  a  capacity  of  1  farad 
and  a  coil  of  many  turns  to  have  a  self-induction  of  1  henry.  Sub- 
divisions of  the  farad  and  henry  are  in  practical  use. 

Multiples  and  subdivisions  of  the  other  units  are  also  frequently  used, 
and  for  this  purpose  the  prefixes  kilo,  meaning  1000;  mega,  meaning 

1,000,000;   milli,   meaning  ,   and   micro,   meaning  ^  QQO  Qo()  ,  are 


added  to  the  units,  and  such  terms  as  — 

kilowatt       =1,000  watts, 
megohm       =1,000,000  ohms, 

millivolt       = 


milliampere  =  --.--AA    ampere, 


millihenry    =   -       henry, 


microfarad=i^oiooofarad' 

second, 


are  in  common  use.  The  most  common  practical  units  of  capacity  and 
self-induction  (the  qualities  of  electric  circuits  with  which  wireless 
telegraphy  is  principally  concerned,  because  they  determine  the  period 
of  vibration)  are  the  microfarad  and  the  millihenry,  but  even  these  are 
too  large  for  convenience. 

The  terms  mil,  meaning  —  i-  inch;  micron,  meaning  1  Q00  ^  meter; 

circular  mil,  meaning  area  of  a  wire  having  a  diameter  of  j^  inch, 

are  also  in  general  use  among  electricians. 

92.  The  E.  M.  F.  (volts)  in  any  circuit  connected  with  a  dynamo 
depends  only  on  the  rate  of  cutting  of  lines  of  force  (strength  of  field 
and  rate  of  revolution). 


62  MANUAL    OF    WIRELESS    TELEGRAPHY. 

The  resistance  (ohms)  in  any  circuit  depends  only  on  the  material, 
cross  section,  and  length  of  the  conductor  forming  the  circuit. 

The  current  (amperes)  in  any  circuit  depends  only  on  the  E.  M.  F. 
and  the  resistance  in  the  circuit. 

The  power  (watts)  in  any  circuit  depends  only  on  the  E.  M.  F.  and 
current  in  the  circuit. 

The  self-induction  (henries)  in  any  circuit  depends  only  on  the  shape 
and  length  of  the  circuit,  on 'the  magnetic  permeability  (art.  25)  of  the 
material  surrounding  and  inclosed  by  the  circuit,  and  on  the  amount  of 
this  material. 

The  capacity  (farads)  in  any  circuit  depends  only  on  the  shape  and 
area  of  its  surface,  on  the  electric  permeability  (art.  46)  of  the  material 
surrounding  the  circuit,  on  the  amount  and  location  of  this  material  (the 
dielectric),  and  on  the  position  of  the  circuit  relative  to  other  conductors. 

(Straight  wires  are  said  to  have  distributed  inductance  and  capacity, 
coiled  wires  have  concentrated  inductance,  and  condensers  have  con- 
centrated capacity. ) 

The  coulombs  in  a  charged  condenser  or  circuit  depend  only  on  the 
capacity  and  potential  of  the  condenser  or  circuit. 

93.  From  the  foregoing  we  can  make  up  a  table  of  values  as  follows : — 

A  volt  =  100,000,000  =  108  absolute  units  of  E.  M.  F. 

An  ohm  =  1,000,000,000  =  109  absolute  units  of  resistance. 

An  ampere  —  -^  =  10^  absolute  units  of  current. 

A  watt— a  volt  x  an  amp.  =  108x  10~1  =  107  absolute  units  of  work 
per  second=  1  joule  per  second  =  TJ^-  H.  P.  =  0.737  foot-pounds  per 
second. 

A  horse  power  =746  watts. 

A  kilowatt=1000  watts. 

A  farad=  1,000,000,000  =10~9  absolute  units  of  capacity' 

A  farad  in  electro-static  units  =  9x!011  centimeters. 

A  microfarad  =  1  farad  =1Q-15  absolute  units  of  capacity. 

A  microfarad  in  electro-static  units  =  900,000  centimeters. 

A  henry  =  1,000,000,000  =109  absolute  units  of  self-induction. 

A  millihenry  =  —- —  henry  =  106  absolute  units  of  self-induction. 

1UUU 

A  millihenry  in  electro-magnetic  units  =  1,000,000  centimeters. 

A  standard  Leyden  jar  or  plate  having  a  capacity  of  .002  microfarad 
has  been  adopted  for  naval  use.  In  electro-static  notation  1  standard  jar 
has  a  capacity  of  1800  centimeters. 


Chapter  III. 

CAPACITY,  SELF-INDUCTION  AND  MUTUAL  INDUCTION  IN 
WIRELESS  TELEGRAPH  CIRCUITS. 

FUNDAMENTAL  EQUATION   OF  WIRELESS  TELEGRAPHY. 

94.  It  was  stated  in  art.  56  that  the  period  of  electrical  vibration  of 
any  circuit  depends  only  on  the  capacity  and  self-induction  of  the  circuit. 

When  the  ratio  of  the  resistance  to  the  self-induction  of  a  circuit  is 
small,,  and  the  circuit  vibrates  in  its  own  period,  the  period  is  found  to 
be  equal  in  seconds  to  2?rV LC  (3)  when  L  is  measured  in  henries,  C  is 
measured  in  farads,  71-  =  3. 1416.  This  is  called  the  fundamental  equation 
of  wireless  telegraphy.  (See  table  7,  appendix  A.) 

If  R  is  greater  than  2  J  ^    the  circuit  will  not  vibrate  at  all.     For 

V  c 

instance,  when  a  condenser  is  discharged  through  a  wire  of  great  resist- 
ance the  charge  leaks  out  slowly  without  any  oscillation. 

A  nonoscillatory  condenser  discharge,  as  compared  with  an  oscillatory 
discharge,  is  like  the  flow  of  molasses  into  a  jar  as  compared  with  a  large 
and  sudden  flow  of  water  into  a  similar  jar.  One  takes  up  a  position  of 
equilibrium  slowly  but  surely,  while  the  other  vibrates  and  splashes  and 
only  settles  down  after  a  considerable  period. 

Equation  (3)  shows  that  a  circuit  having  a  self-induction  of  1  henry 
and  a  capacity  of  1  farad  would  have  a  period  of  ZTT=  6.2832  seconds. 
Its  wave  length  would  be  1,168,000  miles. 

The  standard  wave  length  originally  adopted  for  naval  wireless  tele- 
graph circuits  was  320  meters;  the  period  was  approximately  -g-jnnnnr 
second,  that  is,  they  made  approximately  900,000  complete  vibrations 
per  second.  The  usual  capacity  in  these  circuits  was  0.014  microfarad 
(seven  0.002  microfarad  jars  in  parallel).  Therefore  the  self-induction 
must  have  been  0.0022  millihenry. 

It  will  be  noted  that  the  period  of  a  circuit  varies  as  the  square  root 
of  the  product  of  the  inductance  and  capacity,  so  that  doubling  either 
of  these  increases  the  period  by  V2,  i.  e.,  to  1.414  times  its  former 
value.  Doubling  both  inductan'ce  and  capacity  doubles  the  period. 

SELF-INDUCTION. 

95.  We  see  that  all  conductors  must  have  self-induction,  because  we 
know  that  all  currents  are  surrounded  by  magnetic  fields  produced  by 


64  MANUAL   OF    WIRELESS    TELEGRAPHY. 

the  currents.  The  production  of  the  field  creates  an  E.  M.  F.  in  the 
circuit  opposite  in  direction  to  the  E.  M.  F.  causing  the  current  and 
tending  to  stop  it,  so  that  self-induction  has  been  defined  in  a  qualitative 
manner  as  the  inherent  quality  of  electric  currents  which  tends  to  impede 
the  introduction,  variation,  or  extinction  of  an  electric  current  passing 
through  an  electric  circuit. 

It  has  also  been  expressed  in  quantity  as  the  number  of  lines  of  force 
induced  in  a  circuit  by  the  establishment  of  unit  current  in  it.  It  bears 
the  same  relation  to  electricity  as  inertia  does  to  matter;  it  represents 
its  resistance  to  change  of  condition,  and  it  might  be  defined  as  the  work 
necessary  to  create  unit  current  in  a  circuit. 

Suppose  we  wish  to  determine  the  work  done  in  creating  a  current  of 
value  I  in  a  circuit  of  self-induction  L  in  a  time  T. 

Since  L=the  counter  E.  M.  F.  of  self-induction  when  the  current  is 
varied  at  the  rate  of  1  ampere  per  second,  the  counter  E.  M.  F.  when 

it  is  varied  at  the  rate  of  -„-  amperes  per  second  =  —  - .     If  the  rise 

in  current  is  uniform,  the  counter  E.  M.  F.  is  uniform  and  the  total 
work  done  (which  equals  the  product  of  the  E.  M.  F.,  current,  and 

time)  would  be  equal  to  -~  x!xT=LI2,  were  it  not  for  the  fact  that 


j- 


the  current  rises  uniformly  from  zero  to  7  and  its  mean  value  is  -=-    and 

/v 
T  72 

therefore  the  work  done=  =^-  (4).     Since  the  factor  of  time  does  not 

appear  in  the  result  it  shows  that  it  requires  the  same  amount  of  work 
to  create  a  given  current  in  a  circuit  of  given  self-induction  whether 
it  is  created  slowly  or  quickly,  and  that  this  work  is  equal  in  'joules  to 
one-half  the  product  of  the  self-induction  in  henries  by  the  square  of 
the  current  in  amperes.  Therefore  in  a  circuit  whose  self-induction  is 
2  henries  the  work  done  in  creating  a  steady  current  of  10  amperes  is 

O    NX    1  A2 

equal  to  -         -  =  100  joules  =  73.7  foot-pounds. 

<v 

This  73.7  foot-pounds  represents  the  energy  stored  in  the  magnetic 
field;  it  is  the  work  done  by  the  circuit  in  creating  its  own  field.  If  it 
is  in  the  neighborhood  of  other  circuits  the  momentary  current  created 
in  them  during  the  rise  of  current  reacts  on  the  field  and  makes  the 
amount  of  work  required  still  greater. 

When  the  current  is  broken  the  collapse  of  the  field  restores  this 
energy  to  the  circuit,  thus  tending  to  prolong  the  current, 

In  alternating  currents,  where  the  rise  and  f-all  is  continuous,  the 
magnetic  field  is  continually  absorbing  or  giving  out  energy.  In  oscil- 
lating circuits  the  energy  is  constantly  changing  from  magnetic  to 
electric  and  vice  versa. 


MANUAL  OF  WIRELESS  TELEGRAPHY.  65 

CAPACITY. 

96. .  Now  suppose  we  wish  to  determine  the  work  done  in  charging 
a  condenser  of  capacity  C  to  a  voltage  or  potential  E  in  a  time  T.  The 
potential  of  the  condenser  is  zero  before  charging  begins  and  increases 
as  the  charge  increases,  so  that  the  resistance  to  charging  also  increases 
with  the  charge;  therefore  it  must  take  more  work  to  add  a  coulomb  of 
electricity  to  a  condenser  of  high  than  to  one  of  lower  potential. 

The  total  quantity  of  electricity  in  coulombs  in  the  condenser  is 
Q=E  C,  and  assuming  that  the  condenser  is  charged  at  a  uniform  rate, 

CF 

the  coulombs  per  second  flowing  into  it=^=-,  and  this  must  equal  the 

amperes  in  the  charging  circuit.  The  condenser  being  charged  at  a 
uniform  rate,  its  potential  will  rise  uniformly  from  zero  to  E  and  the 
total  work  done  during  the  time  T  must  equal  the  average  potential 

4-  xrate  of  chargextime  =  |-  X  ^  X  T  =  ^  (5). 

A  </  JL  a 

Since  the  factor  of  time  disappears,  this  shows  that  it  requires  the 
same  amount  of  work  to  charge  a  given  condenser  to  a  given  potential 
whether  it  is  charged  slowly  or  quickly,  and  that  this  work  is  equal  in 
joules  to  one-half  of  the  product  of  the  capacity  in  farads  by  the  square 
of  the  potential  in  volts. 

Therefore,  in  a  circuit  whose  capacity  is  2  farads,  the  work  done  in 

charging  it  to  a  potential  of  10  volts  =  2  X  1Q2  =100  joules  =  73. 7  foot- 

& 

pounds.  We  see  that  it  takes  the  same  amount  of  work  to  charge  a 
condenser  whose  capacity  is  2  farads  to  a  potential  of  10  volts  as  it 
does  to  create  a  current  of  10  amperes  in  a  circuit  whose  self-induction 
is  2  henries. 

If  the  capacity  of  the  condenser  is  2  microfarads  instead  of  2  farads, 
the  required  work  is  one-millionth  of  73.7  foot-pounds  =  0.000073 7  foot- 
pounds. 

This  73.7  foot-pounds  represents  the  energy  stored  in  the  electric  field, 
just  as  the  73.7  foot-pounds  in  art.  95  represented  the  energy  stored  in 
the  magnetic  field. 

Disregarding  losses  it  is  the  amount  of  work  the  condenser  can  do  on 
discharge. 

COMBINATION  OF  SELF-INDUCTION  AND  CAPACITY  IN  OSCILLATING 

CIRCUITS. 

97.  In  an  oscillating  circuit,  when  the  condenser  is  discharged — i.  e., 
when  the  coatings  are  at  zero  potential — the  electric  energy  has  been 
transformed  into  magnetic  energy.  If  there  were  no  losses  in  the  con- 


66  MANUAL    OF    WIRELESS    TELEGRAPHY. 

denser  due  to  heating,  radiation,  etc.,  the  conversion  would  be  perfect, 
the  work  in  the  magnetic  field  of  the  circuit  referred  to  in  art.  95 
would  equal  73.7  foot-pounds,  and  this,  in  turn,  would  be  again  trans- 
formed into  electric  energy  when  the  condenser  recharges.  (See  art.  54.) 
A  magnetic  field  can  not  be  maintained  steadily  except  by  a  current, 
but  a  condenser  can  be  charged  and  kept  in  that  condition  for  some 
time.  However,  condensers  used  in  wireless  telegraphy  are  always  dis- 
charged immediately,  and  the  energy  stored  in  them  before  discharge  is 
the  stock  in  trade,  so  to  speak,  of  the  sending  apparatus;  it  represents 

the  work  it  can  do  on  the  ether. 

j^ 

98.  Keeping  in  mind  our  five  equations — /  =  -— -  (1);  P  =  IE   (2); 

period  (T)=27rVLC  (3)  ;  W=^f  (4)  ;  and  W  =  ^  (5). 

Let  us  consider  a  condenser  having  a  capacity  of  0.02  microfarad 
(10  standard  jars  in  parallel)  charged  to  a  potential  of  30,000  volts. 

9    X/    OA   f)f)A 

Such  a  condenser  would  contain  '         =0.0006  coulomb,  and 

2  X  108  X  9  X  10~8 
would  be  capable  of  doing  work  equal  to  -          — ^ —          -  =9  joules 

=  6.64  foot-pounds. 

If  this  condenser  is  discharged  through  a  circuit  having  a  self-induc- 
tion of  such  value  (0.00125  millihenry)  as  will  give  a  wave  length  of 
300  meters,  the  frequency  of  the  circuit  is  1,000,000,  the  alternations 
2,000,000  per  second,  and  0.0006  coulomb  will  create  in  such  a  circuit 
a  momentary  current  of  2,000,000  x  0.0006  =  1200  amperes. 

If  this  energy  is  radiated  in  five  complete  oscillations,  the,  rate  of 
doing  work,  if  the  efficiency  of  conversion  is  unity,  is  9  joules  in  l  -$-3%-$-$^ 
second  =1,800,000  per  second=1800  kilowatts. 

This  shows  that  though  the  available  energy  is  very  small,  the  rate  of 
doing  work,  that  is,  the  power  of  a  wireless  telegraph  sender,  may  be 
very  great  for  an  exceedingly  short  period  of  time. 

EFFICIENCY  OF  SENDING  APPARATUS. 

99.  We  can  not,  however,  utilize  the  whole  of  the  energy  stored  in  the 
condenser  on   account  of  unavoidable   losses  which  will   appear  later. 
With  a  certain  wireless  telegraph  set  on  which  experimental  measure- 
ments were  made,  Fleming  found  the  actual  power  radiated  to  be  about 
10$  of  that  supplied  to  the  transformer  and  20$  of  that  supplied  to  the 
condenser.* 

*  Journal  Institution  of  Electrical  Engineers,  vol.  44,  London,  April,  1910. 


MANUAL    OF    WIRELESS    TELEGRAPHY.  67 

Professor  Fessenden  and  Dr.  L.  W.  Austin  in  the  Brant  Eock  experi- 
ments found  that  with  the  set  on  which  measurements  were  made  about 
75$  of  the  power  delivered  to  the  spark  gap  was  given  to  the  antenna. 

Very  few  complete  investigations  of  this  kind  have  been  made. 

EFFICIENCY  OF   RECEIVING  APPARATUS. 

100.  Fessenden  in  his  published  account  of  his  experiments  on  the 
sensitiveness  of  wireless  telegraph  detectors  states  that  in  the  most  sen- 
sitive detectors  the  least  amount  of  work  which  will  render  a  signal 
readable  is  .007  erg  per  dot. 

If  a  dot  lasts  --^-  of  a  second  this  represents  approximately  .01  erg 
-Lo 

per  second,  or  -^-^-  watts. 

Dr.  L.  W.  Austin's  tests  of  telephones  in  1908,  several  years  subsequent 
to  Fessenden's  experiment,  indicate  that  to  produce  audible  sound  in  a 

telephone  required  not  less  than  j^j  watts.    With  telephones  of  the  sen- 

3 

sitiveness  previously  available  it  required  not  less  than  ---Q  watts. 

The  6.64  foot-pounds  of  work  which  the  condensers  under  considera- 
tion can  release  equals  90,000,000  ergs.  With  a  radiation  efficiency  of 
20$,  if  about  one  billionth  part  of  this  can  be  concentrated  on  the 
receiving  apparatus,  the  signals  sent  out  can  be  read. 

DIFFERENCE  BETWEEN  DIRECT  AND  ALTERNATING  CURRENTS  DUE  TO  SELF- 
INDUCTION   AND   CAPACITY. 
•p 

101.  The  fundamental  electric  equation  /  =  -=-  is  derived  from  meas- 

H 

urements  of  the  relations  existing  between  electric  current  and  a  con- 
stant E.  M.  F.  in  a  circuit  of  constant  resistance. 

Self-induction  only  affects  a  current  when  it  is  being  started  or 
stopped.  It  increases  the  time  it  takes  for  the  current  to  rise  to  its 
steady  value  and  the  time  it  takes  to  fall  to  zero.  For  continually 
changing  currents  both  in  strength  and  direction  it  impedes  both  rise 
and  fall,  and  therefore  acts  as  a  resistance,  so  that  the  resistance  of  a 
circuit  for  alternating  currents  is  not  the  same  as  for  steady  or  direct 
currents,  but  is  a  combination  of  the  ohmic  resistance  and  the  induc- 
tive resistance  or  reactance  (art.  30).  Keactance  is  not  a  true  ohmic 
resistance,  which  appears  as  heat,  but  is  rather  a  counter  or  opposing 
E.  M.  F. 

The  action  is  still  further  complicated  in  circuits  having  capacity, 
as  wireless  telegraph  circuits  have,  since  capacity  is  found  to  assist  both 


68  MANUAL   OF    WIRELESS    TELEGRAPHY. 

the;  rise  and  fall  of  current,  and  therefore  to  act  in  an  opposite  direction 
to  the  self-induction  and  to  decrease  the  total  resistance  or  impedance. 

T7I 

In  alternating  circuits  we  have  1=   —  where  Z  =  fhe  impedance  = 

Z 

LI  R*-\-\  2nNL  --  N  being  the  frequency  of  the  alternating 

!3*jV  C 


current. 

Since   capacity   and   inductance   produce    opposite    effects,   they    can 

be  used  to  neutralize  each  other,,  if  2-n-NL  =  the  equation  becomes 

-pi 

7=  -=-  as  for  direct  currents,  E  being  the  instantaneous  value  of  the 
H 

E.  M.  F. 

In  circuits  where  the  resistance  and  capacity  are  very  small,  and  the 
self-induction  comparatively  large,  as  in  priman^  sending  circuits, 
Z  =  approximately  2-n-NL,  or  the  current  depends  almost  entirely  on  the 
reactance  of  self-induction.  The  current  in  wireless  telegraph  sending 
circuits  is  sometimes  governed  by  reactance  regulators  placed  in  the 
primary  circuit.  (See  art.  30.) 

TIME  CONSTANTS  OF  CONDENSERS  AND  INDUCTIVE  CIRCUITS. 

102.  Every    capacity    and   inductance   has   what   is    called    its    time 
constant. 

The  time  constant  of  a  condenser  is  equal  to  C  R  —  i.  e.,  the  product 
of  its  capacity  and  the  resistance  through  which  it  is  charged.  If  C  is 
measured  in  microfarads,  R  must  be  measured  in  megohms,  and  their 
product  will  then  be  in  seconds.  The  greater  the.  time  constant  of  a 
condenser  the  longer  time  it  will  take  for  it  to  arrive  at  a  given  fraction 
of  the  charging  potential. 

For  any  usual  transformer  charging  frequency  this  effect  is  inappre- 
ciable. 

The  time  constant  of  an  inductive  circuit  =  -^  .    The  greater  the  time 

H 

constant  of  a  circuit  the  longer  it  takes  to  establish  a  current  of  a  given 
strength  in  it. 

SKIN   EFFECT  IN   HIGH-FREQUENCY   ALTERNATING   CURRENTS. 

103.  Another  effect  of  alternating  currents  on  the  apparent  resistance 
of  circuits  is  seen  when  the  frequencies  are  above  100.     It  is  called  by 
Fleming  the  phenomenon  of  skin  or  surface  resistance.     The  current 
seems  to  begin  at  the  surface  of  a  conductor  and  soak  in,  and  to  penetrate 
to  the  center  it  must  have  time.    This  is  another  instance  of.  the  time 
effect  that  must  be  kept  in  mind  when  dealing  with  alternating  and  oscil- 


MANUAL    OF    WIRELESS    TELEGRAPHY.  69 

lating  currents.  Lord  Rayleigh  has  investigated  this  effect  and  finds  that 
for  wires  made  of  nonmagnetic  material  of  diameter  d  the  ratio  between 
the  resistance  for  frequencies  of  a  million  to  the  steady  resistance  is 

-^  =  ?JL  ^  1,000,000  where  p=the  specific  resistance  of  the  wire. 

If  the  wire  is  of  iron  its  resistance  for  high-frequency  currents  is  still 
greater. 

The  resistance  of  No.  16  wire  for  frequencies  of  a  million  is  6.5  times 
greater  than  its  steady  resistance.  The  larger  the  diameter  of  the  wire 
the  greater  the  proportional  increase  in  resistance.  Stranded  wire, 
having  proportionally  greater  surface  than  solid  wire  of  the  same  area 
of  cross  section,  offers  less  resistance  to  high-frequency  currents. 

Flat  ribbons,  haviifg  larger  surface,  offer  less  resistance  than  circular 
wire  of  the  same  area  of  cross  section. 

In  the  Stone  receiving  circuits,  the  inductance  coils  were  wound  with 
wire  of  such  size  that  for  the  frequency  intended  the  current  penetrated 
to  the  center  and  there  was  no  wasted  material..  Resistance  is  decreased 
by  using  a  number  of  strands  in  parallel. 

Currents  in  wireless  telegraph  circuits  having  a  wave  length  of  300 
meters  penetrate  about  T\  millimeter,  or  approximately  ^J-g-  inch,  inside 
the  surface  of  the  conductor.  If  the  wires  are  of  iron  the  current  pene- 
trates about  -g-ffVo'  inch. 

We  see,  therefore,  that  oscillating  currents  used  in  wireless  telegraphy, 
especially  those  in  the  closed  circuit,  not  only  may  be  very  large  for  a 
very  short  period  of  time,  but  that  they  remain  practically  on  the  surface 
of  the  conductor,  and  it  is  evident  that  the  latter  should  have  much 
greater  area  than  would  be  necessary  to  prevent  heating  by  the  same 
steady  current. 

CAPACITY    AND    SELF-INDUCTION    OF    STRAIGHT    WIRES. 

104.  The  capacity  and  self-induction  of  all  but  very  simple  forms  of 
circuits  are  very  difficult  to  calculate,  and  in  general  they  are  deter- 
mined by  comparison  with  known  values. 

The  capacity  of  a  straight,  vertical  wire  of  length  I  and  diameter  d, 
well  above  the  earth  and  away  from  other  conductors,  is  in  microfarads 

0=  -          l 


Fleming  states  that  a  wire  111  feet  long  and  diameter  0.085  inch, 
suspended  vertically,  was  found  to  have  a  capacity  of  0.000205  micro- 
farad, or  approximately  one-tenth  of  one  standard  Ley  den  jar.  Four 
wires  of  the  above  size  and  length,  being  6  feet  apart,  were  found  to  have 
a  capacity  of  0.000583  microfarad,  or  about  three  times  as  much  as  one 
wire. 


70  MANUAL    OF    WIRELESS    TELEGRAPHY. 

One  hundred  and  sixty  such  wires  in  the  shape  of  an  inverted  cone, 
2  feet  apart  at  the  top  and  in  contact  at  the  bottom,  had  a  capacity  of 
only  about  thirteen  times  that  of  a  single  wire. 

It  will  be  seen  that  doubling  the  wire  in  an  aerial  does  not  double  its 
capacity.  For  wires  about  2  feet  apart  the  capacity  increases  approx- 
imately as  the  square  root  of  the  number  of  wires — that  is,  16  wires 
would  give  four  times  the  capacity  of  1  wire. 

The  self-induction  of  a  straight  wire  of  length  /  and  diameter  d  and 
circular  cross  section  at  a  distance  from  other  conductors  is  2  I  (2.3026 

4/ 

log.    ~;j~~l):>   values  being  given  in  centimeters.     The   self-induction 
d 

of  two  parallel  wires  varies  as  the  distance  between  them,  decreasing 
with  the  distance,  so  that  adding  straight  wire  to  a*n  aerial  does  not  add 
to  its  self-induction  in  the  same  proportion. 

The  relation  between  the  inductance  and  capacity  of  a  straight  wire 
of  circular  section  and  diameter  small  in  comparison  with  its  length  is 
such  that  its  electrical  length  is  equal  to  its  natural  length,  and  its  wave 
length  is  therefore  twice  its  natural  length. 

A  vertical  straight  wire,  well  grounded  and  of  small  diameter,  has  an 
apparent  electrical  length  approximately  equal  to  twice  its  natural  length; 
its  wave  length  is  approximately  four  times  its  natural  length. 

Pierce  states  that  a  single  wire  100  feet  long  and  -J  inch  diameter, 
when  alone  in  space  has  as  much  capacity  as  an  isolated  flat  metallic  disc 
16  feet  in  diameter.* 

CONDENSERS  IN  SERIES  AND  IN  PARALLEL. 

105.  When  two  or  more  condensers  are  placed  in  parallel  (fig.  28c), 
their  total  capacity  C  is  equal  to  the  sum  of  their  capacities  taken  singly ; 


*j 


°^ 
c4 


FIG.  28c.  FIG.  28D. 

i.  e.,  C  =  Oj  +  C2  +  etc.  When  two  equal  condensers  are  placed  in  series 
(fig.  28d),  the  resulting  capacity  is  one-half  of  that  of  each  taken  singly, 
or  in  general 


*  Principles  of  Wireless  Telegraphy,  by  G.  W.  Pierce,  A.M.,  Ph.D.  (1910). 


MANUAL    OF    WIRELESS    TELEGRAPHY.  71 

A  condenser  is  often  placed  in  large  aerials  to  shorten  the  natural 
wave  length  for  receiving.  The  aerial  in  this  case  being  considered  as 
one  plate  of  a  condenser  and  the  earth  the  other,  when  a  condenser  is 
placed  between  the  aerial  and  the  earth  we  have  two  condensers  in  series. 

Condensers  which  will  be  ruptured  if  used  alone  can  be  used  in  series, 
dividing  the  voltage  between  them. 

For  instance,  take  a  transformer  giving  30,000  volts  to  be  used  in  con- 
nection with  condensers  that  will  stand  but  20,000,  by  placing  2  in  series 
each  condenser  would  have  to  stand  but  15,000  volts. 

It  will  be  seen  that  32  jars  made  up  into  2  condensers  of  16  jars,  in 
parallel,  in  each  and  the  two  condensers  placed  in  series  would  only  have 
the  capacity  of  a  single  condenser  of  8  jars  in  parallel,  but  the  work 
on  each  jar  would  be  four  times  lighter. 

106.  If  a  straight  wire  is  broken  in  the  middle  the  oscillation  period  of 
each  half  would  be  half  the  original  period  were  it  not  for  the  fact  that 
the  adjacent  ends  of  the  wire  and  the  air  between  them  form  a  small 
condenser  which  has  the  effect  of  slightly  increasing  the  capacity  of  each 
half,  thus  giving  it  a  period  slightly  longer  than  half  of  the  original 
period. 

From  the  above  it  appears  that  we  can  shorten  the  electrical  length  of 
an  aerial  (radiating  circuit,  art.  75,  fig.  29)  by  putting  a  condenser  in 
series  with  it,  but  we  can  not  shorten  it  to  less  than  one-half  its  original 
period. 

We  know  that  by  coiling  the  wire  we  can  increase  its  self-induction 
and,  therefore,  its  electrical  length  and  wave  length  with  very  little 
increase  in  its  physical  length.  In  practice,  wave  lengths  of  the  closed 
circuit  (art.  75)  are  altered  by  changing  their  self-induction  as  above. 
The  wave  lengths  of  the  open  circuit  (aerial)  are  increased  by  adding 
inductance.  They  are  decreased  by  adding  condensers  in  series  (for 
receiving  only). 

MEASUREMENT  OF  INDUCTANCE  AND  CAPACITY  IN  OSCILLATING  CIRCUITS. 

107.  By  comparison  with  standard  inductances  and  capacities,  the 
capacity  and  self-induction  of  circuits  can  be  measured  and  their  periods 
calculated. 

Measured  inductances  and  capacities  connected  together  so  as  to  form 
an  oscillating  circuit  are  made  so  that  the  capacity  or  inductance  (usually 
the  capacity)  or  both  are  variable.  They  can  be  calibrated  so  as  to  show 
directly  either  the  period  or  wave  length  of  the  circuit  for  any  position  of 
the  variable  elements. 

If  brought  near  another  circuit  in  which  electrical  oscillations  are 
taking  place  and  adjusted  so  as  to  have  a  maximum  of  current  induced 
the  two  circuits  are  said  to  be  in  tune  or  resonance.  (They  have  the 


72  MANUAL    OF    WIRELESS    TELEGRAPHY. 

same  electrical  length.)     When  used  as  above,  calibrated  oscillating  cir- 
cuits are  called  ivave  meters,  ondameters  or  cymometers. 

Wave  meters  can  be  so  arranged  as  to  measure  separately  the  induc- 
tance or  capacity  of  oscillating  circuits  as  well  as  their  periods.  If  a 
spark  gap  forms  part  of  the  oscillating  circuit,  its  period  can  also  be 
directly  measured  by  measuring  the  time  between  the  successive  surgings 
of  the  spark.  This  is  done  by  photographing  the  sparks  by  reflection 
from  the  surface  of  a  rapidly  revolving  mirror.  The  movement  of  the 
mirror  between  sparks  separates  their  images  on  the  photographic  film, 
and  knowing  the  number  of  revolutions  of  the  mirror  per  second,  the 
elapsed  time  between  sparks  can  be  calculated  and  hence  the  period  of  the 
circuit. 

INDUCTANCES. 

108.  In  sending  circuits  the  capacities  (condensers)  are  usually  fixed 
and  the  wave  lengths  are  varied  by  varying  the  inductance  (self-induc- 
tion).    This  usually  consists  of  a  bare  copper  wire,  tube,  or  ribbon 
coiled  so  as  to  form  a  helix.     Of  course  the  self-induction  of  such  a  coil 
could  be  very  greatly  increased  by  providing  it  with  an  iron  core,  but  the 
magnetic  hysteresis  loss   (art,  148)  would  be  too  great.     The  magnetic 
hysteresis  loss  in  air,  like  the  dielectric  hysteresis  loss,  is  practically  zero ; 
therefore,  these  inductances  have  air  cores  and  as  much  of  their  length  is 
included  in  the  circuit  as  will,  in  connection  with  the  fixed  capacity 
(condensers),  give  the  wave  length  desired.     (See  fig.  73  for  photograph 
of  sending  helix.) 

MUTUAL  INDUCTION  AND  ITS  EFFECT  ON  OSCILLATING  CIRCUITS. 

109.  Mutual  induction  between  two  circuits  is  explained  in  art..  15.    It 
is  represented  by  the  letter  M  and  is  defined  as  the  E.  M.  F.  generated  in 
one  circuit  when  the  current  in  the  other  circuit  is  varied  at  the  rate  of 
one  ampere  per  second.     The  two  circuits  are  coupled  together  by  virtue 
of  their  mutual  induction  and  the  induced  current  represents  a  transfer 
of  energy  from  one  circuit  to  the  other. 

If  their  mutual  induction  is  large,  they  are  said  to  have  close  or  tight 
coupling;  if  small,  the  coupling  is  said  to  be  loose.  It  is  evident  that  the 
mutual  induction  between  two  circuits  depends  on  the  self-induction  of 
each,  that  is,  the  strength  of  the  magnetic  fields  produced  by  varying 
the  current.  Also  that  it  depends  on  the  distance  apart  of  the  two 
circuits  and  the  material  (iron  or  air)  intervening.  It  is  a  maximum 
when  all  the  lines  of  force  created  by  the  current  in  either  circuit  cut  the 
other.  In  this  case  the  coupling  is  said  to  be  perfect.  If  the  two  circuits 
in  the  case  of  perfect  coupling  have  the  same  self-induction  their  mutual 
induction  is  equal  to  the  self-induction  of  each;  if  different  the  mutual 
induction  in  such  a  case  is  equal  to  V L±L2,  L±  being  the  self-induction 
of  one  circuit,  L2  that  of  the  other. 


MANUAL    OF   WIRELESS    TELEGRAPHY.  73 

If  the  two  circuits  are  moved  in  relation  to  each  other  so  that  only  part 
of  the  magnetic  field  created  by  each  cuts  the  other,  their  mutual  induc- 
tion is  decreased. 

The  ratio  of  the  mutual  induction  (for  any  position  of  the  circuits)  to 
its  maximum  value  is  called  the  coefficient  of  coupling  for  that  position, 

or  coefficient  of  coupling  =     _  =. 


The  mutual  induction  between  two  oscillating  circuits  alters  the  effec- 
tive self-induction  of  each  (art.  92),  making  it  apparently  larger  or 
smaller  as  one  circuit  is  receiving  energy  from  or  transferring  energy  to 
the  other. 


110.  Since  the  natural  period  of  a  circuit  in  seconds  —  ^ir^jLG  (3), 
if  L,  the  effective  self-induction,  is  varied,  the  period  of  the  circuit  is 
varied. 

Coupled  circuits  having  the  same  or  nearly  the  same  natural  periods 
are  found  to  have  two  periods  of  oscillation,  one  faster  and  the  other 
slower  than  the  natural  period  of  each.  Therefore  the  open  radiating 
circuit  sends  out  electric  waves  of  two  lengths,  one  longer  and  one  shorter 
than  the  natural  wave  length  of  the  circuit.  The  closer  the  coupling  the 
greater  the  difference  in  length  of  these  two  waves.  This  difference 
divided  by  the  natural  wave  length  of  the  circuit  is  called  the  per- 
centage of  coupling.  This  can  be  more  easily  ascertained  than  the 
coefficient  of  coupling.  For  instance,  if  an  open  circuit,  having  a  natural 
wave  length  (as  determined  by  a  wave  meter)  of  400  meters  sends  when 
coupled  to  a  closed  circuit  of  the  same  natural  length  two  waves,  one  of 

445,  the  other  365  meters,  the  percentage  of  couplings  —  ^——  —  =  20$. 

111.  If  the  circuits  have  loose  coupling,  i.  e.,  are  moved  farther  apart, 
the  mutual  induction  is  less  and  the  difference  in  the  wave  length  radiated 
is  less.     This  distance  can  be  increased  until  the  two  waves  practically 
coincide  with  the  natural  wave  length  of  the  circuit.    This  is  very  loose 
coupling,  but,  since  without  mutual  induction,  no  energy  can  be  trans- 
ferred, the  two  can  never  be  the  same. 

Most  of  the  energy  is  found  to  be  in  the  longer  wave  and  until 
recently  that  in  the  short  wave  was  practically  wasted.  The  method  now 
used  of  generating  but  one  wave  length  will  be  described  under  sending 
apparatus. 


Chapter  IV. 


ELECTEIC  OSCILLATIONS  AND  3ADIATIOX  OF  ELECTRIC 

WAVES. 

112.  It  has  been  stated  that  every  oscillating  circuit  must  contain 
inductance  and  capacity.  This  is  true  even  though  the  circuit  consists  of 
straight  wires,  for  these  have  distributed « inductance  and  capacity.  If 
the  circuit  is  formed  as  in  fig.  26a  with  a  coil  of  wire  and  a  condenser, 
the  inductance  and  capacity  are  said  to  be  concentrated  or  lumped.  There 
is  also  a  certain  amount  of  distributed  inductance  and  capacity,  but  in 
general  this  will  be  small  compared  with  the  concentrated  portions. 


FIG.  26A. 


FIG.  30. 


FIG.  31. 


FIG.  26A. — Non-radiating  Circuit. 

FIG.  30. — Radiating  Circuit. 

FIG.  31. — Electric  Wave  Leaving  Oscillator. 

In  the  case  of  a  linear  oscillator  (fig.  30),  when  the  oscillations  are 
taking  place  and  the  charges  are  most  widely  separated,  we  may  imagine 
lines  of  electric  force  to  be  connecting  each  unit  of  positive  electricity  on 
one  end  to  a  unit  of  negative  electricity  on  the  other.  For  clearness  of 
conception  we  may  picture  these  lines  of  force  as  having  a  real  exist- 
ence and  exerting  an  elastic  pull  between  the  positive  and  negative  units, 
tending  to  draw  them  together,  while  at  the  same  time,  provided  they 
are  running  in  the  same  direction,  they  tend  to  repel  each  other.  These 
lines  of  force  in  the  case  of  a  linear  oscillator,  on  account  of  their 
repulsion  away  from  the  oscillator,  form  wide  loops  which  tend  to  snap 
off  and  travel  away  into  space  when  the  charges  again  rush  back  through 


MANUAL    OF    WIRELESS    TELEGRAPHY. 


75 


the  spark  gap,  thus  forming  electrical  waves  or  radiation  as  shown  in 
fig.  31.  In  the  case  of  the  circuit  shown  in  fig.  26a,  where  the  principal 
capacity  lies  in  the  condenser,  the  lines  of  force  are  concentrated  between 
the  condenser  plates.  They  do  not  loop  out  to  any  extent,  and  hence 
such  a  circuit  radiates  very  feebly.  On  account  of  these  differences  an 
open  circuit  oscillator  (fig.  30)  is  often  called  a  radiating  circuit,  while 
a  closed  circuit  (fig.  26a)  is  called  non-radiating,  although  all  high 
frequency  circuits  radiate  in  some  degree. 

113,  Let  fig.  32  represent  a  closed  circuit  inductively  connected  to  a 
vertical  grounded  open  circuit  or  aerial,  and  suppose  the  spark  gap  to 
break  down  at  the  point  of  maximum  potential  of  the  charging  current. 
At  this  instant  there  is  no  current  in  the  closed  circuit  and,  therefore, 
no  current  in  the  open  circuit.  The  energy  is  all  electro-static,  all  in  the 
closed  circuit  and  practically  all  in  the  electro-static  field  between  the 
condenser  plates,  the  capacity  of  the  spark  points  and  other  parts  of  the 
circuit  being  very  small. 


? 


FIG.  32. 


FIG.  32A. 


As  soon  as  discharge  through  the  spark  gap  commences  the  field  of  the 
current  in  the  closed  circuit  inductance  induces  movements  of  electric 
charges  in  the  open  circuit,  the  starting  point  of  the  disturbance  being 
the  open  circuit  inductance.  As  the  charges  in  the  open  circuit  separate 
they  are  connected  by  electro-static  lines  of  force  and  surrounded  by 
magnetic  lines  of  force,  both  moving  outward  at  the  same  rate  that  the 
charges  move  in  a  straight  wire. 

The  electro -static  field  becomes  a  maximum  when  the  charge  reaches 
the  top  of  the  wire.  At  this  time  the  magnetic  field  is  a  minimum.  At 
the  expiration  of  a  half  period,  when  the  charges  meet  again,  the  mag- 
netic field  is  a  maximum,  but  reversed  in  direction.  The  electro-static 
6 


76  MANUAL    OF    WIRELESS    TELEGRAPHY. 

field  reverses  as  the  charges  separate  again.  If  they  can  be  represented 
as  meeting  in  the  open  circuit  inductance,  the  electro-static  field  just  after 
the  end  of  a  half  period  can  be  represented  as  in  fig.  32a,  where  the 
mutual  repulsion  of  the  electro-static  lines  of  force  outside  the  wire  has 
kept  them  from  returning  as  fast  as  the  charges  travel  towards  each 
other.  As  the  charges  meet,  the  ends  of  the  lines  of  electric  force  unite 
and  become  closed  circuits,  or  electric  whorls  shaped  like  smoke  rings 
which,  owing  to  the  mutual  repulsion  of  all  their  parts,  expand  outward, 
upward,  and  downward. 

It  is  in  some  such  manner  that  we  can  conceive  energy  to  be  detached 
and  sent  out  into  space  from  wires  forming  oscillating  circuits. 

The  expanding  rings  touch  the  earth  and  are  guided  by  it  as  by  any 
other  conductor,  thus  resembling  near  the  earth  expanding  hemispherical 
shells. 

These  may  be  called  earthed  waves  to  distinguish  them  from  the  free 
waves  which  exist  momentarily  in  the  vicinity  of  an  ungrounded 
oscillator. 

114.  If  the  point  of  connection  with  the  closed  circuit  is  considered 
as  at  the  earth,  earthed  waves  only  are  generated  and  detached  from  the 
aerial  and  no  free  waves  exist  at  any  time.  The  production  of  earthed 
electric  waves  under  these  conditions  is  illustrated  in  fig.  33. 


FIG.  33.— Earthed  Electric  Waves. 

We  know  that  earthed  waves  are  guided  by  conducting  surfaces;  we 
know  that  light  waves  are  not;  we  do  not  know  where  the  dividing  line 
is  between  waves  that  are  radiated  in  straight  lines  and  those  that  are 
guided  by  conductors. 

115.  For  simplicity  we  have  described  the  process  of  radiation  in  terms 
of  electro-static  lines  of  force,  but  it  must  not  be  forgotten  that  a  moving 
electro-static  field  always  produces  a  magnetic  field  at  right  angles  to 
itself  and  at  right  angles  to  the  direction  of  movement,  so  that  we  have 
electro-static  lines  perpendicular  to  the  surface  of  the  earth  (at  least  near 
the  aerial),  and  magnetic  lines  in  circles  surrounding  the  aerial. 

Both  the  electro-static  and  the  electro-magnetic  fields  reverse  their 
directions  every  half  wave  length. 


MANUAL   OF   WIRELESS   TELEGRAPHY.  77 

r 

The  process  of  radiation  withdraws  energy  from  the  circuit  just  as  is 
the  case  when  a  resistance  is  placed  in  the  circuit;  hence  the  radiation 
resistance  is  an  expression  often  used,  meaning  the  resistance  which  under 
the  given  conditions  would  use  up  the  same  amount  of  energy  as  that 
removed  from  the  circuit  by  radiation.  This  radiation  resistance  depends 
only  on  the  form  and  dimensions  of  the  aerial  and  on  the  frequency  of 
the  oscillations,,  increasing  rapidly  as  the  frequency  increases.  It  is 
independent  of  the  intensity  of  the  oscillations  and  of  other  sources  of 
lost  energy  in  the  circuit. 

Radiation  resistance  might  be  called  the  radiation  coefficient.  Accurate 
means  of  measuring  it  are  not  yet  in  general  use. 

DAMPED  OSCILLATIONS. 

116.  It  has  been  explained  (art.  54)  that  when  a  circuit  consisting  of 
a  condenser,  inductance,  and  spark  gap  is  charged  by  a  transformer  to  a 
potential  so  great  that  a  spark  passes  across  the  gap,  the  electricity  stored 
up  in  the  condenser  discharges  itself  through  the  spark  gap,  and  by  its 
inertia  charges  the  condenser  in  the  opposite  sense,  only  at  the  next 
instant  to  again  discharge  itself,  and  so  on.  All  this  takes  place  during 
the  time  of  one  spark,  and  in  fact  this  surging  of  electricity  is  what  keeps 
the  spark  in  existence  after  the  first  discharge.  This  surging  back  and 
forth  would  continue  indefinitely  were  it  not  for  the  energy  used  up  in 
the  heat  of  the  spark  and  in  the  resistance  and  other  losses  in  the  rest 
of  the  circuit,  But  as  no  new  energy  can  be  introduced  into  the  circuit 
until  the  condenser  is  recharged,  the  electrical  surgings  decrease  in 
intensity  and  finally  cease. 

If  we  represent  time  by  the  horizontal  axis  and  the  amplitude  of  the 
oscillations  by  the  vertical  axis,  fig.  34  will  show  graphically  the  course 


FIG.  34. — Damped  Oscillations.    Energy  Supplied  at  Beginning  of  Wave-train. 

of  the  phenomenon.  It  is  exactly  analogous  to  a  light  pendulum  which 
is  set  swinging  and  which  is  brought  to  rest  after  a  limited  number  of 
swings  by  the  friction  of  the  air. 

Gradually  decreasing  oscillations  of  this  kind  are  called  damped  oscil- 
lations and  obey  the  law  that  each  succeeding  amplitude  is  a  given 
fraction  of  the  one  before  it,  that  is,  the  amplitudes  form  a  geometric 
series. 


78  MANUAL   OF    WIRELESS    TELEGRAPHY. 

117.  For  purposes  of  calculation  it  is  sometimes  convenient  to  make 
use  of  a  system  of  logarithms  which  instead  of  using  10  for  its  base, 
as  is  the  case  with  common  logarithms,  uses  the  number  2.7183.  These 
natural  logarithms  can  always  be  obtained  from  the  common  logarithms 
by  multiplying  the  latter  by  the  factor  2.3026.  If  the  natural  logarithms 
of  the  successive  amplitudes  of  our  oscillations  be  taken,  it  will  be  found 
that  the  successive  logarithms  differ  from  each  other  by  a  constant  num- 
ber. This  number  in  the  present  case  is  known  as  the  logarithmic 
decrement  of  the  oscillations.  Its  chief  interest  to  us  lies  in  the  fact  that 
it  is  a  measure  of  the  energy  losses  in  the  circuit. 

Wave  Natural  logarithms  Wave  Natural  logarithms 

amplitudes          of  the  amplitudes  amplitudes          of  the  amplitudes 

in  the  ratio  (constant  difference^  in  the  ratio  (constant  difference) 
1Q                           S  =  0.223±                                   10  «  =  0.223± 

1000  6.908  410  6.016 

800  6.685  328  5.793 

640  6.462  262  5.569 

512  6.238  210  5.347 

It  is  often  expressed  by  the  symbol  8  (delta).  If  we  express  all  the 
losses  in  the  circuit  in  terms  of  a  resistance  R  which  would  give  us  the 

T> 

equivalent  loss,  8==—=,  where  n  is  the  frequency  and  L  the  induct- 
ance of  the  circuit,  R  and  L  being  expressed  in  corresponding  units,  for 
instance,  absolute  units.  This  formula  enables  us  at  once  to  determine 
the  equivalent  resistance  of  the  circuit  when  the  damping  has  been 
measured.  For  the  derivation  of  this  formula  and  for  the  general  mathe- 
matics of  the  damping  theory,  the  reader  must  be  referred  to  mathe- 
matical works  on  the  subject.  Some  authors  define  8  as  the  logarithmic 
decrement  per  half  oscillation,  but  following  the  more  general  usage  we 
have  defined  it  as  the  decrement  per  whole  oscillation,  that  is,  between 
two  oscillations  in  the  same  direction. 

UNDAMPED   OSCILLATIONS. 

118.  It  has  been  seen  in  the  last  article  that  the  cause  of  the  dying 
out  of  a  train  of  oscillations  in  a  spark  circuit  is  the  using  up  of  energy 
in  the  circuit  together  with  the  fact  that  no  energy  can  be  brought  in 


FIG.  35. — Undamped  Oscillations.     Energy  Constantly  Supplied. 

from  outside  to  compensate  this  loss.  If  means  can  be  found  for  keeping 
up  a  constant  supply  of  energy,  our  oscillations  can  be  made  to  continue 
indefinitely  and  with  equal  amplitude  (fig.  35). 


MANUAL   OF   WIRELESS   TELEGRAPHY. 


79 


119.  The  electric  waves  produced  during  one  set  of  oscillations  are 
called  a  wave  train.  If  more  than  one,  the  wave  trains  produced  during 
one-half  cycle  of  the  charging  current  are  called  a  group  of  wave  trains. 

The  duration  of  a  wave  train  is  the  time  of  one  oscillation  multiplied 
by  the  number  of  oscillations  in  the  train. 

It  is  found  that  the  duration  of  a  wave  train  is  much  less  when  the 
oscillating  circuit  (A,  B,  K,  fig.  29)  is  connected  to  an  aerial  with  one 
end  free  and  the  other  earthed,  like  C  D,  than  when  it  oscillates  without 
any  other  electrical  connection.  The  energy  is  radiated  more  rapidly, 
the  vibrations  more  quickly  damped.  For  this  reason  the  circuit  formed 
by  the  condenser,  spark  gap>  and  inductance  is  called  the  dosed  or  oscil- 
lating circuit;  that  formed  by  the  aerial,  inductance  and  ground,  the 
open  or  radiating  circuit.  (See  art.  75.) 


FIG.  29. 


120.  Considering  the  series  of  expanding  hemispherical  shells  referred 
to  in  art.  113,  and  shown  in  fig.  33,  if  there  is  but  one  wave  train  per 
alternation  of  the  condenser  charging  current,  the  thickness  of  one  of 
these  series  is  equal  to  the  wave  length  multiplied  by  the  number  of  oscil- 
lations per  train.  Suppose  this  to  be  10  and  the  wave  lengths  500  meters, 
then  the  depth  of  a  wave  train  is  5000  meters,  or  a  little  more  than  three 
miles.  If  the  frequency  of  the  alternating  current  is  60  cycles,  or  120 
alternations  per  second,  we  have  120  wave  trains  per  second,  and  since 
they  travel  at  the  rate  of  186,000  miles  per  second  the  wave  trains  have 
intervals  of  1550  miles  between  them,  so  that  working  at  ordinary  dis- 
tances and  this  frequency,  each  wave  train  has  passed  the  receiving 
'station  before  its  successor  has  left  the  sending  station. 

If  the  alternator  frequency  is  500,  the  wave  trains  are  only  186  miles 
apart,  or  about  the  distance  of  ordinary  daylight  communication  between 
ships. 


80  MANUAL   OF    WIRELESS    TELEGRAPHY. 

121.  Professor  G-.  W.  Pierce,  of  Harvard  University,  has  measured  the 
period  of  some  types  of  oscillating  circuits  used  in  wireless  telegraphy, 
and  it  is  from  his  published  account  of  his  experiments  that  the  follow- 
ing description  is  derived. 

Suppose  a  spark  gap  set  to  break  down  at  a  potential  of  10,000  volts, 
to  be  used  in  a  circuit  where  the  maximum  potential  reached  in  the 
condenser  is  30,000  volts. 

Let  the  curve  of  sines  in  fig.  18  represent  the  condenser  potentials 
of  the  oscillating  circuit  during  2  alternations,  each  lasting  y^  of  a 
second. 

The  resistance  of  the  spark  gap  is  practically  infinite  before  the  poten- 
tial reaches  10,000  volts,  and  therefore  no  current  passes.  When  the 
potential  has  risen  to  10,000  volts  the  spark  gap  is  ruptured.  Its  resist- 
ance decreases  instantly  to  a  fraction  of  an  ohm,  and  during  the  first 
half  of  the  oscillation  the  condenser  is  discharged  to  zero  potential.  Dur- 
ing the  last  half  of  the  oscillation  it  is  charged  again  in  the  opposite 
sense.  The  sparks  pass  first  in  one  direction  and  then  in  the  other,  and 
the  spark  gap  not  regaining  its  resisting  qualities,  the  oscillations  or 
surgings  continue  until  the  potential  (owing  to  losses  due  to  the  radiation 
of  energy  in  the  shape  of  electric  waves,  to  heating  the  circuit,  and  the 
light  and  heat  at  the  spark  gap)  does  not  rise  high  enough  to  disrupt 
the  gap. 

The  transformer  immediately  recharges  the  condenser,  which,  as  soon 
as  it  again  reaches  a  potential  of  10,000  volts,  breaks  down  the  spark  gap 
again,  and  a  second  series  of  oscillations  begins. 

In  the  circuit  under  consideration  the  maximum  charging  potential 
is  30,000  volts,  so  that  a  condenser  with  a  spark  gap  breaking  .down  at 
10,000  volts  may  be  charged  and  discharged  several  times  during  one- 
half  cycle  of  the  charging  current. 

The  spark  acts  like  a  trigger  which  suddenly  releases  the  stored 
energy  in  the  condenser,  and  as  soon  as  this  energy  has  been  radiated, 
the  trigger  automatically  resets  itself  and  does  not  release  again  until 
the  condenser  is  recharged. 

It  is  evident  that  if  the  spark  gap  in  the  circuit  under  consideration 
is  adjusted  to  30,000  volts,  but  one  discharge  of  the  condenser  per  alterna- 
tion will  take  place  and  but  one  train  of  waves  will  be  sent  out.  Shorten- 
ing the  gap  will  increase  the  number  of  discharges  per  alternation. 

The  exact  number  for  any  spark-gap  length  will  depend  on  the  time 
of  an  alternation — i.  e.,  the  frequency,  and  on  the  length  of  time  it  takes 
the  available  power  to  charge  the  condenser  to  the  voltage  required  to 
break  down  the  gap.  Less  energy  per  wave  train  will  be  radiated  on  a 
short  gap  than  on  a  long  one,  because  the  work  done  varies  as  the  square 
of  the  voltage  (see  art.  96) ;  but  the  total  work  done  may  be  equal,  on 
account  of  the  greater  number  of  discharges. 


MANUAL    OF    WIRELESS    TELEGRAPHY.  81 

If  the  spark  gap  is  too  short,  an  arc  is  formed  and  no  oscillations  take 
place  except  those  due  to  the  frequency  of  the  charging  current. 

Professor  Pierce  has  shown  that  the  interval  between  wave  trains  may 
vary  on  account  of  the  residual  charge  left  in  the  condenser.  When  the 
spark  gap's  original  resistance  is  restored,  the  potential  of  the  residual 
charge  may  be  opposed  to  the  potential  of  the  transformer  and  delay  the 
charging.  He  has  shown  also  that  the  gap  sometimes  partly  retains  its 
conducting  character  and  breaks  down  at  a  lower  potential  than  its  length 
would  indicate.  This  makes  the  sparks  and  oscillations  irregular  in 
strength  and  number  and  produces  ragged  and  poor  signals. 

In  certain  cases  Professor  Pierce  notes  an  increase  of  received  energy 
of  400  per  cent  when  using  a  Cooper-Hewitt  mercury  interrupter  in  place 
of  an  ordinary  spark  gap. 

122.  With  a  given  power  the  work  that  can  be  done  per  second  is  fixed. 


In  charging  a  condenser  W=—  —  .     The  number  of  times  this  is  done 

/& 

per  second  gives  the  work  per  second,  or  the  power  expended.  By 
increasing  the  frequency  we  can  for  a  given  power  either  reduce  the 
voltage  (length  of  gap)  or  the  capacity  of  the  condenser.  For  instance, 
ai  a  frequency  of  500  cycles,  for  the  same  power,  the  condenser  need  only 
be  1/10  the  size  as  for  a  frequency  of  50  cycles.  Or,  keeping  the  capacity 
the  same,  the  voltage  can  be  reduced  to  I/  V  10=  approximately  1/3  of 
that  necessary  for  the  same  power  at  50  cycles.  A  table  showing  the 
capacities  necessary  for  given  powers  at  different  frequencies  and  voltages 
is  given  in  table  2,  appendix  A. 

123.  When  the  spark  gap  is  set  to  break  down  at  the  maximum  charg- 
ing potential  the  condenser  absorbs  and  stores  all  the  energy  that  can  be 
transferred  by  the  charging  transformer  during  the  alternation.  When 
it  discharges  it  transfers  part*  of  the  energy  to  the  open  circuit  to  be 
radiated  as  electric  waves.  Since  its  period  of  discharge  is  very  short 
as  compared  with  that  of  the  charging  current  the  latter  current  does  not 
appreciably  change  during  the  time  the  condenser  is  discharging.  This 
current  immediately  begins  to  again  charge  the  condenser,  but  the  voltage 
of  the  latter  does  not  rise  high  enough  to  cross  the  gap  so  that  the  con- 
denser soon  begins  to  return  energy  to  the  charging  circuit.  It  does 
this  until  its  potential  and  the  charging  potential  (and  current  if  they 
are  in  phase)  falls  to  zero.  It  then  begins  to  absorb  energy  again  with  the 
reverse  potential,  and  on  reaching  the  maximum  voltage  again  discharges 
across  the'  gap. 

Fig.  36  is  an  attempt  to  illustrate  this  action  graphically.  The  area 
included  by  the  curve  on  the  left  of  the  zig-zag  line  indicates  the  work 

*  Experimentation  has  proven  that  from  80  to  90  per  cent  of  the  energy 
delivered  to  the  transformer  is  transferred  to  the  spark  circuit. 


82 


MANUAL    OF    WIRELESS    TELEGRAPHY. 


done  on  the  condenser  during  the  first  half  of  an  alternation;  the  zig- 
zag line  indicates  the  number  and  amplitude  of  vibrations  made  by 
the  closed  circuit  in  transferring  the  energy  to  the  radiating  circuit. 
The  area  included  by  the  curve  on  the  right  of  the  zig-zag  line  "repre- 
sents the  work  done  during  the  second  half  of  the  alternation  in  recharg- 
ing the  condenser.  This  work  is  all  returned  to  the  charging  circuit. 


FIG.  36. 


MECHANICAL   WORK   DONE   IN    MAKING   DOTS   AND  DASHES   OF   THE   TELE- 
GRAPH CODE. 

124.  We  are  now  in  position  to  speak  in  more  specific  terms  of  the 
work  done  in  sending  wireless  telegrams. 

Let  us  suppose  that  we  are  delivering  2  kilowatts  at  60  cycles  and 
110  volts  to  a  transformer,  which  delivers  it  to  a  condenser  at  a  maxi- 
mum potential  of  30,000  volts. 

Two  kilowatts  =2000  watts  =  2000  joules  per  second  =  1474  foot-pounds 
per  second. 

Since  60  cycles  =  120  alternations  per  second,  the  work  equals  approxi- 
mately 12.3  foot-pounds  per  alternation. 

If  the  work  done  on  the  condenser  is  in  phase  with  the  charging 
E.  M.  F.,  and  if  the  spark  gap  is  set  to  break  down  at  a  potential  of 
30,000  volts,  the  condenser  will  be  discharged  at  the  peak  of  the  charging 
curve,  or  when  one-half  of  the  work  that  can  be  done  in  an  alternation 
(12.3  foot-pounds)  has  been  done  on  the  condenser.  The  capacity  of  a 
condenser  which  takes  12.3  foot-pounds  of  work  to  charge  it  to  30,000 
volts  =  .0372  microfarad,  or  approximately  eighteen  0.002  microfarad 
jars. 

Suppose  we  are  sending  at  the  rate  of  20  words  per  minute,  that  the 
words  average  5  letters  each,  and  that  each  letter  is  made  up  of  3  char- 


MANUAL   OF    WIRELESS    TELEGRAPHY.  83 

acters  equal  in  length  to  9  dots,  then  a  minute  can  be  represented  as 
equal  to  20x5x9  =  900  dots  =  15  dots  per  second.  In  other  words, 
the  length  of  a  dot  is  one-fifteenth  of  a  second.  Now  we  have  120  alter- 
nations per  second,  so  that  we  have  about  8  alternations  per  dot  when 
sending  at  the  rate  of  20  words  per  minute;  therefore  a  dot  is  made  up  of 
8  distinct  sets  of  discharges  of  the  condenser  and  a  dash  of  three  times 
that  number.  The  condenser  is  doing  work  in  producing  ether  waves  at 
the  rate  of  12.3  foot-pounds  per  alternation,  equaling,  approximately,  100 
foot-pounds  per  dot  and  300  foot-pounds  per  dash. 

It  will  be  noted  from  the  text  that  at  this  sending  rate  the  frequency 
necessary  to  give  1  alternation  per  dot  and  2  alternations  per  dash  is  only 
7J  cycles  per  second. 

It  will  be  noted  further  that  with  one  spark  per  alternation  we  cannot 
utilize  2  kilowatts  continuously.  We  can  only  use  it  in  charging  the  con- 
denser during  the  first  half  of  each  alternation.  As  soon  as  the  discharge 
begins  the  condenser  circuit  oscillates  in  its  own  period  as  if  entirely 
disconnected  from  the  transformer. 

In  this  respect  the  charge  and  discharge  of  a  condenser  resembles  the 
loading  and  firing  of  a  gun.  We  must  bear  in  mind,  however,  that 
though  the  charging  may  be  done  at  any  rate  we  desire,  the  discharge  is 
very  much  more  sudden  than  that  of  any  gun. 

It  is  not  necessary,  therefore,  except  when  considering  methods  of 
regulation,  to  devote  attention  to  the  charging  of  the  condenser,  and 
our  minds  can  be  concentrated  on  what  happens  during  its  discharge, 
when  it  forms  part  of  an  oscillating  circuit. 

From  the  foregoing  discussion  we  see  that  the  real  source  of  power  in 
wireless  telegraphy  is  the  condenser,  and  that  we  can  only  use  it  inter- 
mittently, not  more  than  one-fiftieth  of  the  time,  in  fact,  but  that  while 
working  it  works  very  energetically. 

DECREASE  OF  AMPLITUDE  WITH  DISTANCE  FROM  SOURCE. 

125.  From  the  discussion  in  art.  120  on  the  thickness  of  the  hemi- 
spherical shell  enclosing  a  train  of  ether  waves,  if  we  assume  this  thick- 
ness to  remain  constant  and  that  part  of  the  shell  near  the  earth  to  be 
represented  by  an  expanding  cylinder,  it  is  increasing  in  size  by  one 
dimension  only,  viz.,  circumference,  and  therefore  the  energy  in  any  part 
of  this  shell  will  vary  inversely  as  the  distance,  instead  of  inversely  as  the 
square  or  cube  of  the  distance  from  the  source,  as  would  be  the  case  if 
expansion  were  taking  place  in  two  or  in  three  directions. 

Messrs.  W.  Duddell  and  J.  W.  Taylor  in  experiments  made  for  the 
English  Navy  in  1905  proved  that  at  least  for  distances  up  to  60  miles 
the  received  current  as  stated  above  varies  inversely  as  the  distance  from 
the  sending  station,  and  the  received  energy  varies  inversely  as  the  square 


84  MANUAL    OF    WIRELESS    TELEGRAPHY. 

of  the  distance.  But  additional  experiments  by  Dr.  L.  W.  Austin  show 
that  this  law  does  not  hold  except  for  very  short  distances,  and  that  the 
amplitude  is  lessened  from  other  causes  than  those  due  to  distance  alone. 
We  know  that  the  energy  is  absorbed  in  the  atmosphere  more  by  day- 
light than  by  night — more  at  high  (summer)  than  at  low  (winter)  tem- 
peratures. The  amount  of  absorption  as  between  one  day  and  another 
probably  depends  also  on  the  electric  condition  of  the  atmosphere. 
Long  waves  suffer  less  absorption  than  short  ones.  Irregular  country 
produces  large  absorption.  The  absorption  over  some  soils  is  for  com- 
paratively long  distances,,  30  times  as  great  as  over  sea  water.  Trans- 
mission over  salt  water  is  the  best. 

126.  As  illustrating  the  difference  in  absorption  between  short  and  long 
waves,  and  (a)  the  greater  efficiency  of  short  waves  for  short  distances, 
(b)  the  rapid  falling  off  at  distances  above  100  miles,  Dr.  Austin  finds : 

(a)  Strength  of  received  signals  at  20  miles,  using  300  meter  waves, 
5  times  as  great  as  with  1500  meter  waves;  at  100  miles,  300  meter  waves, 
4  times  as  great  as  1500  meter  waves;  at  400  miles,  300  meter  waves,  1.6 
times  as  great  as  1500  meter  waves;  at  800  miles,  signals  from  300  meter 
waves  weaker  than  from  1500  meter  waves. 

(b)  Using  300  meter  waves,  strength  of  signals  at  200  miles,  0.3  of 
that  at  100  miles;  at  400  miles,  0.053  of  that  at  100  miles;  at  800  miles, 
0.0036  of  that  at  100  miles.     (See  table  11,  appendix  A.) 

DETECTION  OF  ELECTRIC  WAVES. 

127.  The  direction  of  the  magnetic  lines  of  force  at  any  point  in  a  wave 
near  the  earth  is  parallel  to  the  earth's  surface  and  at  right  angles  to  a 
line  joining  the  point  with  the  source  of  radiation.    The  direction  of  the 
electro-static  lines  of  force  at  any  point  near  the  earth  is  perpendicular 
to  the  earth's  surface. 

An  iron  wire  placed  horizontally  and  parallel  to  the  lines  of  magnetic 
force  will  be  magnetized  by  a  passing  electric  wave  just  as  iron  wires  held 
in  the  magnetic  meridian  become  magnetized ;  pointed  in  the  direction  of 
the  station  the  effect  would  be  zero.  It  has  been  proposed  to  utilize  this 
fact,  both  as  a  detector  of  electric  waves  and  of  their  direction. 

Any  conducting  wire  held  perpendicular  to  the  earth  will  be  cut  at 
right  angles  by  the  magnetic  lines  of  force  and  will  have  electric  charges 
induced  in  it  which  will  create  currents,  and  it  is  by  means  of  the  cur- 
rents induced  in  vertical  conductors  that  electric  waves  are  usually  de- 
tected. A  vertical  wire  thus  situated  also  has  a  difference  of  potential 
created  in  its  ends  since  it  joins  two  points  of  the  advancing  wave  whose 
electric  potential  differs.  (This  may  also  be  the  case  in  a  horizontal  wire 
if  in  the  line  joining  its  position  with  the  source  of  radiation.) 

The  total  electric  is  equal  to  the  total  magnetic  energy  in  an  advancing 
wave. 


MANUAL    OF    WIRELESS    TELEGRAPHY.  85 

If  two  horizontal  conducting  plates  forming  a  condenser  are  in  the 
path  of  the  wave,  they  will  have  electro-static  charges  of  different  poten- 
tials induced  in  them.  This  potential  difference  will  vary  with  their 
vertical  distance  apart.  If  these  plates  are  joined  by  a  conductor,  electric 
currents  will  be  produced  in  it. 

We  see,  therefore,  that  there  should  be  at  least  three  ways  of  detecting 
electric  waves:  (a)  By  placing  conductors  at"  right  angles  to  the  mag- 
netic field;  (b)  By  placing  conductors  parallel  to  the  electric  field;  (c) 
By  adding  to  conductors  at  right  angles  to  the  magnetic  field,  conducting 
planes  forming  condensers  at  right  angles  to  the  electric  field. 

It  would  seem  that  by  the  last  method  we  should  be  able  to  abstract  the 
greatest  amount  of  energy  from  an  electric  wave  and,  therefore,  be  able 
to  detect  it  at  the  greatest  distance  from  its  source. 

128.  It  will  readily  be  seen  that  the  induction  of  currents  in  another 
aerial,  however  great  the  distance  from  the  inducing  aerial,  is  not  greatly 
different  from  the  inductive  actions  of  the  wires  A  B  and  C  D  on  each 
other,  which  was  discussed  in  the  early  part  of  this  book. 

It  was  there  pointed  out  that  inductive  actions  caused  by  ether  move- 
ments could  have  no  limits,  however  small  they  might  be  at  great  dis- 
tances. In  other  words,  every  change  of  current  sends  out  some  non- 
returnable  energy.  Oscillating  circuits  of  high  frequency  send  out  more 
non-returnable  energy  and  radiate  better  than  those  of  low  frequency. 
Open  oscillating  circuits  radiate  faster  than  closed  oscillating  circuits. 


Chapter  V. 

SENDING  CIECUITS  AND  APPARATUS. 

129.  We  shall  now  proceed  to  consider  wireless  telegraph  sets  in  detail : 

GENERATORS. 

Induction  coils  (fig.  14b)  with  hammer  breaks  operated  b}7  direct  cur- 
rent have  been  used  to  a  very  limited  extent  for  naval  purposes.  The 
vibrations  of  the  hammer  were  difficult  to  regulate  and  the  large  size 
necessary  to  handle  large  currents  made  the  frequency  too  low  for 
successful  work.  Hammer  breaks  were  soon  discarded  and  make  and 
break  regulated  by  some  form  of  rotary  motion.  The  most  successful 
form  was  the  mercury  turbine  interrupter.  This  interrupter  was  installed 
in  the  circuit  containing  the  sending  key  and  the  primary  winding 
of  the  induction  coil.  The  interrupter  consisted  of  a  direct-current 
motor  driving  a  centrifugal  pump  revolving  in  a  chamber  of  mercury. 
The  mercury  was  connected  to  one  side  of  a  break  in  one  leg  of  the 
primary  circuit.  It  was  drawn  up  by  the  pump  and  delivered  as  a  jet 
through  a  revolving  nozzle.  The  mercury  jet  during  a  portion  of  each 
revolution  struck  a  metallic  segment  connected  to  the  other  side  of  the 
break  in  the  circuit,  and,  if  the  sending  key  was  closed,  thereby  completed 
the  circuit  and  built  up  a  current  in  the  induction  coil  which  charged  the 
sending  condensers.  When  the  jet  passed  the  segments  the  circuit  was 
broken.  (The  jet  passed  through  grain  alcohol  which  absorbed  the  spark 
at  break.)  This  make  and  break  occurred  once  in  each  revolution.  The 
motor  made  approximately  1800  revolutions  per  minute.  Assuming  that 
the  condenser  was  discharged  only  on  the  break,  this  gave  but  30  dis- 
charges per  second,  or  a  note  two  octaves  *  lower,  as  compared  with  120 
discharges  from  a  60-cycle  alternator.  The  operation  of  these  sets  was 
much  improved  by  increasing  the  number  of  segments  and,  therefore,  the 
number  of  makes  and  breaks  per  second,  as  many  as  six  being  used,  thus 
giving  a  spark  note  slightly  higher  than  that  of  a  60-cycle  alternator. 

The  spark  in  the  interrupter  at  break  always  carbonized  some  alcohol 
and  the  latter  also  became  mixed  with  mercury  and  formed  a  more  or  less 

*  The  octave  of  a  note  is  that  differing  from  it  by  8  notes  of  the  scale 
— do-re-mi-fa-sol-la-si-do — the  octave  above  having  twice  as  many  vibrations 
per  second  and  the  octave  below  having  one-half  as  many  vibrations  as  the 
note  referred  to.  Standard  tuning  forks  vibrate  256  times  per  second.  The 
pitch  of  a  note  is  the  number  of  vibrations  per  second  producing  that  note. 


MANUAL   OF   WIRELESS   TELEGRAPHY.  87 

conducting  carbon-mercury-alcohol  emulsion,  so  that  the  interrupter  and 
contents  required  frequent  cleaning,  washing,  and  filling. 

For  small  powers  these  sets,  with  care,  gave  good  results,  and  being 
generally  used  with  mechanical  recording  apparatus  the  spark  note  was 
not  of  marked  importance. 

CONSIDERATIONS  GOVERNING  FREQUENCY  OF  GENERATORS. 

130.  Turbine  interrupters  were  practically  entirely  replaced  by  60- 
cycle  alternating  current  generators  operated  by  motors  (on  ships  and  at 
navy  yards)    or  oil  engines    (isolated  shore  stations  and  light  ships). 
These  in  turn  are  being  replaced  by  500-cycle  sets  operated  by  motors  or 
engines  as  above.    No  special  description  of  generators  will  be  given. 

Sixty-cycle  current  was  first  selected  because  alternators  of  this  fre- 
quency were  commercial  articles.  When  the  use  of  telephones  with  receiv- 
ing sets  became  general  it  was  realized  that  a  sound  of  a  higher  note  was 
desirable  and  that  for  the  very  best  results  the  frequency  (pitch)  of  this 
note  should  be  that  to  which  the  telephone  diaphragm  or  the  operator's 
ear,  or  both,  were  most  sensitive.  A  pure  spark  note  is  produced  when 
the  spark  gap  is  so  adjusted  that  the  condenser  discharges  but  once  per 
alternation,  thus  sending  out  but  one  wave  train  per  alternation. 

THE  ADVANTAGES  OF  A  HIGH  SPARK  FREQUENCY. 

131.  If  two  alternating  currents  of  the  same  intensity  but  of  different 
frequencies  be  sent  through  a  telephone,  it  is  found  that  the  sound  in 
the  telephone  produced  by  the   current  of  higher  frequency   is  much 
louder  than  that  produced  by  the  lower.    This  fact  is  due  in  part  to  the 
peculiarities  of  the  human  ear,  which  is  more  sensitive  to  high-pitched 
sounds  than  to  low,  also  in  part  to  the  diaphragm  of  the  telephone,  which 
is  usually  of  such  a  weight  and  size  as  to  vibrate 'most  readily  to  a  sound 
of  rather  high  pitch.     This  fact  has  an  important  bearing  on  wireless 
telegraphy,  for  the  pitch  of  the  sound  produced  in  the  telephone  con- 
nected to  the  detector  at  the  receiving  station  depends  simply  on  the 
number  of  wave  trains  per  second  at  the  sending  station.     In  order  to 
determine  exactly  what  is  the  relation  between  the  strength  of  current 
required  to  produce  an  audible  sound  in  the  telephone  and  the  frequency, 
a  series  of  experiments  was  carried  out  on  a  pair  of  head  telephones  of 
the  type  ordinarily  used  in  wireless  telegraphy,  the  results  of  which  are 
shown  in  the  table. 

Frequency  Volts  to  Frequency  Volts  to 

per  produce  per  produce 

second.  audible  sound.  second.  audible  sound. 

60  6200  X  10-7  540  80  X  10-7 

120  2900        "  660  30 

180  1700        "  780  11 

300  600        "  900  6 

420  170 


88  MANUAL    OF    WIRELESS    TELEGRAPHY. 

In  the  first  column  are  given  the  frequencies  or  the  number  of  wave 
trains  per  second,  and  in  the  second  the  number  of  volts  of  alternating 
current  which  it  would  be  necessary  to  apply  to  the  terminals  of  the  tele- 
phone to  produce  an  audible  sound.  From  this  it  is  seen  that  it  requires 
about  a  thousand  times  as  much  voltage  at  a  frequency  of  60  to  produce 
a-  sound  as  is  required  at  a  frequency  of  900.  We  may  assume,  therefore, 
that  if  the  number  of  wave  trains  at  the  sending  station  be  increased  from 
60  to  900  per  second,  and  the  spark  length  be  kept  the  same,  the  effect 
at  the  receiving  station  would  be  increased  one  thousand  times.  If  the 
number  of  sparks  be  increased  in  this  way  without  reducing  the  spark 
length,  it  is  evident  that  the  energy  made  use  of  at  the  sending  station 
must  be  greatly  increased.  It  will  be  more  interesting,  therefore,  to 
calculate  what  the  increase  in  sending  efficiency  of  the  station  will  be 
with  increasing  spark  frequency  if  the  total  energy  be  kept  constant.  So 
if  we  assume  that  the  energy  is  proportional  to  the  number  of  wave  trains, 
and  divide  the  relative  increase  in  loudness  of  sound  in  the  telephone  at 
the  receiving  station  for  any  frequency  by  the  relative  increase  in  the 
number  of  wave  trains  per  second,  we  will  have -a  fair  comparison  of  the 
efficiencies  at  the  two  frequencies. 

Strength  Strength 

Frequency.  of  Frequency.  of 

signal.  signal. 

120  1  540  13 

240  1.5  900  64 

The  results  of  such  calculations  are  seen  in  the  table,  which  shows  that 
there  would  be  very  slight  advantage  in  replacing  a  60-cycle  alternator 
giving  120  wave  trains  per  second  with  a  120-cycle  giving  240  wave 
trains,  but  that  the  advantage  increases  rapidly  as  the  frequency  is 
increased.  The  maximum  sensitiveness  of  the  telephone  appears  to  lie  in 
the  neighborhood  of  900. 

132.  In  addition  to  the  increase  of  sensitiveness  of  the  telephone  at 
high  frequencies,  there  are  other  quite  independent  advantages  in  the 
use  of  a  high-pitched  spark.  First,  it  is  found  in  practice  that  a  high- 
pitched  musical  signal  is  much  more  readily  distinguished  at  the  receiving 
station  in  the  midst  of  ordinary  interference  and  atmospheric  disturb- 
ances; and  second,  at  the  sending  station  a  shorter  spark  gap,  which 
would  generally  be  used  with  a  high  frequency  spark,  puts  less  strain  on 
the  insulation  of  the  condensers  and  other  parts  of  the  circuit,  and  re- 
duces the  losses  due  to  brush  discharges,  which  in  many  stations  amount 
to  a  considerable  share  of  the  total  amount  of  power  employed. 

A  third  advantage  is  that  with  a  high  spark  frequency  larger  amounts 
of  energy  can  be  radiated  from  a  moderate-sized  aerial  without  sub- 
jecting it  to  excessively  high  potentials. 

Experiments  have  been  recently  carried  out  in  which  it  has  been  shown 
that  in  moderate  frequencies  with  stationary  spark  gaps  there  are 


MANUAL   OF   WIRELESS   TELEGRAPHY.  89 

nearly  always  secondary  discharges,  irregular,  but  giving  very  high  tones, 
so  that  the  real  advantage  of  the  high  spark  frequency,  from  the  stand- 
point of  telephone  sensitiveness,  is  usually  less  than  that  indicated  in 
the  table.  The  advantages  of  ease  of  reading,  the  lessening  of  the  strain 
on  the  condensers  and  insulators,  and  the  increase  in  effective  energy 
capacity  of  the  antenna,,  especially  when  the  latter  is  small,  are  very 
marked,  so  that  it  has  been  found  possible  to  use  small  wireless  sets  of  2 
K.  W.  capacity  where  formerly  5  to  10  K.  W.  were  employed. 

The  only  difficulty  involved  in  using  very  high  spark  frequencies  lies 
in  the  cooling  of  the  spark  gap.  For  this  purpose  a  rotary  gap  or  some 
special  refrigerating  device  must  be  used. 

133.  For  the  reasons  stated  above,  500  cycles  has  been  adopted  as  a 
standard  frequency  for  the  present. 

An  examination  of  table  2,  appendix  A,,  will  show  how  capacity  for  the 
same  power  decreases  directly  as  the  frequency  increases,  or  keeping' 
power  and  capacity  the  same,  how  voltage  can  be  decreased  with  increase 
of  frequency.  Condensers  are  more  efficient  when  worked  at  a  voltage 
below  that  which  will  give  brush  discharges. 

134.  To  ensure  a  perfectly  regular  condenser  discharge  and  thus  obtain 
but  one  wave  train  per  alternation,  some  generators  have  a  disk  mounted 
on  an  extension  of  the  main  shaft  and  revolving  with  it.     This  disk 
carries  projecting  electrodes,  one  for  each  pole  of  the  alternator,  equally 
spaced  like  the  spokes  of  a  wheel  and  connected  to  one  side  of  the  closed 
circuit.     (See  fig.  52.)     In  revolving  they  pass  very  close  to  a  fixed  elec- 
trode, or  spark  point,  connected  to  the  other  side  of  the  circuit,  sparking 
taking  place  as  the  points  pass — one  series  of  oscillations  for  each  alter- 
nation.    Generators  carrying  rotary  spark  points  must  of  necessity  be 
placed  in  or  near  the  operating  room  and  are  to  that  extent  objectionable 
on  account  of  the  noise  of  the  spark,  the  additional  space  required,  and 
the  noise  of  revolution  which  interferes  with  receiving. 

Motor  generators,  or  generators '  driven  by  engines,  except  as  stated 
above,  are  usually  arranged  for  being  started  or  stopped  from  a  distance. 
The  controlling  apparatus  is  mounted  on  a  switchboard  which  carries 
voltmeters  and  ammeters,  one  each  for  the  supply  current  and  one  each 
for  the  generator  current.  A  frequency  meter  is  also  part  of  the  switch- 
board equipment.  This  with  the  field  rheostat  of  the  motor  enables  the 
operator  to  adjust  the  speed  of  revolution  so  as  to  give  the  required 
frequency. 

TRANSFORMERS. 

135.  A  generator  designed  for  a  certain  frequency  works  best  in  con- 
nection with  a  transformer  designed  for  the  same  frequency.     If  the 
size  of  the  condenser  to  be  used  in  the  closed  circuit  is  fixed,  and  known 
to  the  designer  of  the  transformer,  the  latter  can  be  built  so  that  the 


90  MANUAL    OF    WIRELESS    TELEGRAPHY. 

secondary  winding  and  condenser  form  a  circuit  whose  natural  period  is 
that  of  the  generator  frequency ;  a  few  such  transformers  have  been  sup- 
plied and  are  preferred  to  those  requiring  reactance  regulators.  Neither 
generator  nor  transformer  will  work  without  overheating  at  a  frequency 
much  greater  than  that  for  which  they  are  designed  on  account  of  the 
increase  of  heating  in  the  iron  cores  and  frames,  with  increase  of  cycles 
of  magnetization  per  second. 

An  examination  of  fig.  29  will  show  that  the  generator  armature  wind- 
ing and  the  primary  winding  of  the  transformer  form  one  circuit,  and 
the  secondary  winding  and  condenser  another.  The  reactances  of  these 
circuits  should  be  such  as  to  maintain  the  charging  B.  M.  F.  and  current 
in  phase  with  each  other. 

When  60-cycle  current  was  the  standard,  transformer  windings  were 
designed  to  give  a  potential  of  from  25,000  to  30,000  volts  in  the 
secondary  when  the  primary  was  supplied  with  110-volt  current. 

With  the  reduction  in  voltage  made  practicable  by  the  use  of  higher 
frequency,  standard  transformers  now  have  a  maximum  voltage  of  12,500 
when  supplied  with  220-volt  current. 

For  small  sets  both  induction  coils  and  closed  core  transformers  are 
satisfactory;  for  large  sets  closed  core  transformers  are  preferred. 
Transformers  are  fitted  with  safety  spark  gaps  set  at  the  maximum  safe 
sparking  potential. 

REGULATION  OF  A.  C.  SENDING  APPARATUS. 

136.  Sending  sets  work  most'  efficiently  when  the  interruptions  or 
alternations  of  current  are  in  resonance  with  the  circuit  formed  by  the 
secondary  of  the  transformer  and  the  sending  condenser. 

When  running  on  open  circuit  practically  no  work  is  being  done  by 
the  motor  or  generator  except  that  necessary  to  overcome  friction. 

When  the  primary  circuit  is  closed  by  the  sending  key,  with  the  spark 
gap  opened,  so  that  no  sparking  takes  place,  the  secondary  of  the  trans- 
former charges  the  condenser  during  the  first  half  of  each  alternation 
and  receives  current  from  the  condenser  during  the  second  half  of  each 
alternation. 

The  load  thrown  on  the  motor  generator  by  pressing  the  key  depends 
on  the  period  in  a  cycle  at  which  contact  is  made,  but,  generally  speaking, 
it  may  be  considered  as  instantaneous  "  full  load." 

If -the  spark  gap  is  set  so  that  the  condenser  potential  breaks  it  down, 
the  oscillations  of  the  closed  sending  circuit  practically  cut  out  the 
secondary  of  the  transformer,  so  that  a  condition  of  instantaneous  "  no 
load"  exists  as  soon  as  the  spark  passes.  As  soon  as  these  oscillations 
cease,  the  secondary  again  begins  to  charge  the  condenser,  and  a  condi- 
tion of  almost  instantaneous  full  load  is  established.  This  interval  is 


MANUAL   OF    WIRELESS    TELEGRAPHY.  91 

so  short  that  the  inertia  of  the  moving  parts  of  the  motor  generator  pre- 
vents any  change  of  speed  or  voltage,  so  that  the  instantaneous  full  load 
thrown  on  when  the  key  is  closed  is  the  one  affecting  operation.  Again, 
the  inertia  of  the  moving  parts  of  the  motor  generator  is  often  sufficient 
to  keep  up  the  voltage  during  the  length  of  a  dot,  but  not  during  the 
length  of  a  dash.  > 

When  the  key  is  closed  the  momentary  current  starting  at  that  instant 
depends  only  on  the  reactance  of  the  primary  of  the  transformer  and  of 
the  generator  armature,  since  the  resistance  is  very  low. 

To  control  this  sudden  rush  of  current  an  adjustable  choke  coil,  called 
a  reactance  regulator,  may  be  placed  in  the  primary  circuit.  This  coil, 
on  account  of  its  inertia,  acts  as  a  buffer  against  sudden  changes  of  cur- 
rent, and  by  means  of  its  adjustability  enables  the  phase  relation  of  the 
E.  M.  F.  and  current  in  the  circuit  to  be  varied  and  thus  the  power 
expended  to  be  controlled. 

Since  the  reactance  regulator  controls  the  power  expended,  it  controls 
the  secondary  voltage  and  the  maximum  spark  gap  that  can  be  used. 

By  placing  the  sending  key  in  shunt  around  it  and  having  an  inductive 
resistance  in  series  with  the  key,  the  reactance  regulator  can  be  adjusted 
so  that  no  sparking  will  take  place,  but  by  closing  the  key  the  current 
added  through  the  shunt  circuit  is  sufficient  to  cause  sparking  to  take 
place.  By  means  of  this  method  the  sudden  changes  from  full  to  no 
load  are  avoided  and  the  regulation  improved,  and  since  only  a  small 
portion  of  the  total  sending  current  is  broken  at  the  sending  key,  it  is 
much  easier  to  keep  the  contacts  in  good  condition. 

A  safety  switch  is  placed  in  the  primary  lead  when  the  method  of  con- 
trol described  above  is  installed.  This  switch  should  only  be  closed  when 
sending  and  should  be  opened  at  all  other  times  when  the  motor  genera- 
tor is  running. 

A  better  method  of  control  now  being  introduced  is  to  have  the  send- 
ing key,  by  working  auxiliary  contacts,  strengthen  the  fields  of  the  motor 
and  alternator  by  cutting  out  resistance  just  before  the  primary  circuit 
is  closed. 

The  charge  and  discharge  of  the  condenser  when  not  sparking  is  indi- 
cated by  a  rustling  sound,  which  signifies  danger.  This  warning  applies 
equally  to  induction  coils  and  transformers,  both  terminals  of  which  are 
dangerous  when  using  alternating  current. 

On  account  of  the  small  penetrating  effect  of  high-frequency  currents 
(art.  103),  it  is  believed  that  high  voltages  when  associated  with  fre- 
quencies of  above  100,000  per  second  are  not  dangerous  to  human  life, 
but  low  frequency,  high-voltage  currents  are  very  dangerous,  and  it  must 
be  borne  in  mind  that  a  condenser  being  charged  and  discharged  at  the 
7 


92  MANUAL    OF    WIRELESS    TELEGRAPHY. 

alternator  frequency  is  very  much  more  dangerous  than  when  it  is  dis- 
charging across  the  spark  gap. 

Other  methods  of  generating  high  frequency  currents  are  in  use  than 
by  charging  condensers  through  transformers  and  discharging  them 
through  spark  gaps.  But  since  other  methods  have  not  yet  been  practi- 
cally applied  in  the  United  States  to  any  great  extent,  they  will  not  be 
discussed  in  this  chapter. 

SENDING  KEYS. 

137.  The  sending  key,  or  the  auxiliary  key  operated  by  it,  is  placed  in 
one  leg  of  the  primary  circuit. 

When  placed  directly  in  the  primary  circuit,  sending  keys,  in  some 
cases,  have  condensers  shunted  around  them  to  absorb  the  spark  at  break. 
Their  contacts  when  used  to  break  the  primary  current  direct,  are 
larger  than  in  the  ordinary  telegraph  key  on  account  of  the  larger  cur- 
rents handled.  In  other  respects  they  resemble  the  telegraph  key.  When 
used  to  operate  a  relay  the  ordinary  telegraph  key  fills  all  requirements. 
The  relay  consists  of  a  solenoid  energized  by  the  sending  key,  its  arma- 
ture making  and  breaking  the  primary  current  in  air  or  oil. 

Figs.  37,  38,  38a  and  39  illustrate  types  of  sending  keys.  The  Slaby 
Arco  keys  shown  in  fig.  37  were  of  massive  construction  and  very  rugged. 
Fig.  38  shows  a  solenoid  break,  the  connections  for  which  are  illustrated 
by  fig.  38a.  It  will  be  noted  that  this  is  a  positive  break  as  well  as  make. 
Fig.  39  is  practically  the  same  as  the  ordinary  telegraph  key  with  large 
contacts. 

Sending  keys  should  be  adjusted  to  have  just  sufficient  movement  to 
prevent  arcing  and  permit  well  defined  making  and  breaking^ 

For  direct  breaking,  though  platinum  contacts  are  largely  used,  com- 
paratively large  brass  or  silver  contacts  are  satisfactory.  All  contacts 
must  be  kept  smooth  and  clean  and  their  faces  parallel. 

What  is  known  as  a  "  break  key  "  is  preferred.  It  was  first  used  on 
the  Stone  sets,  and  is  an  ingenious  and  useful  device  for  "  listening  in  " 
while  sending.  An  attachment  to  the  sending  key  breaks  the  detector 
circuit  just  before  the  sending  key  makes  contact.  When  the  sending 
key  is  released  the  receiving  circuit  is  automatically  cut  in,  so  that  the 
receiver  can  "  break  "  the  sender  by  a  call,  which  the  latter  can  hear  in 
the  interval  between  his  letters  or  words. 

For  sending  time  signals,  a  Western  Union  relay  closes  a  local  battery 
having  in  circuit  a  solenoid,  whose  armature  carries  a  lever  which  presses 
and  releases  the  sending  key  in  unison  with  the  current  impulses  sent 
from  the  standard  clock  at  the  Naval  Observatory. 


MANUAL    OF    WIRELESS    TELEGRAPHY. 


93 


FIG.  37.— Slaby  Arco  Key. 


FIG.  38. 


OF  CONNECTIONS 


(TO 


TO  TRANSFORMER 
PRIMARY 


TO  l|0  VOLTS  J).C. 


FIG.  38A. — Solenoid  Key. 


FIG.  39. — Wireless  Specialty  Apparatus  Co. 


94  MANUAL    OF    WIRELESS    TELEGRAPHY. 

CLOSED   CIRCUITS    (INDUCTANCE,   CAPACITY,   SPARK  GAP) . 

138.  Sending  circuits  are  illustrated  by  elementary  diagrams  in  figs. 
29a  and  40  to  48  inclusive.     The  names  under  these  figures  are  the 
names  of  the  engineers  proposing  or  designing  sets  with  the  connections 
shown. 

To  render  them  capable  of  adjustment  all  wireless  telegraph  oscillat- 
ing circuits  have  either  variable  inductances  or  condensers  or  both. 
These  condensers  and  inductances  vary  greatly  in  design.  Those  for 
sending  circuits,  especially  on  account  of  the  high  potentials  to  which  they 
are  subjected,  are  very  different  in  construction  and  mounting  from  those 
used  in  receiving  circuits. 

Fixed  condensers  and  variable  inductances  are  used  in  sending  cir- 
cuits. The  condensers  may  be  single,  two  or  more  in  series,  or  in  parallel. 
Series  parallel  installations  may  be  made  also,  just  as  in  primary  bat- 
teries. (See  figs.  28c  and  28d.) 

The  variable  inductance  usually  consists  of  a  helix  of  comparatively 
large  bare  wire  (round  or  flat)  mounted  on  an  insulating  frame  a  foot  or 
more  in  diameter,  the  turns  of  wire  varying  from  about  f"  to  2"  apart. 
(See  fig.  73.) 

A  large  number  of  the  sending  circuits  in  use  at  present  are  direct  con- 
nected, but  inductively  connected  sets  are  equally  efficient  and  have  this 
advantage  that  the  coupling  can  be  varied  by  a  movement  of  either  the 
closed  or  the  open  circuit  inductance  as  a  whole  without  varying  the  wave 
length  of  either  circuit.  (Figs.  42,  43,  and  45.) 

139.  In  direct  connected  sets,  three  movable  clips  or  sliders  are  usually 
provided,  one  for  the  closed  and  two  for  the  open  circuit  (fig.  40).    The 
closed  circuit  is  permanently  connected  to  one  end  of  the  helix  and  the 
circuit  completed  by  means  of  the  wire  from  the  movable  clip,  which  can 
be  connected  to  any  desired  point. 

The  open  circuit  has  the  ground  and  the  aerial  wire,  respectively, 
attached  to  the  other  two  clips  and  these  are  attached  to  such  points  of 
the  helix  as  will  give  the  open  circuit  the  same  natural  period  as  the 
closed  circuit  and  at  the  same  time  give  the  two  circuits  the  number  of 
turns  in  common  necessary  for  the  desired  coupling. 

140.  In  inductively  connected  sets,  the  closed  circuit  helix  is  the  same 
as  before,  the  open  circuit  helix  is  permanently  attached  to  the  ground 
lead  and  the  aerial  lead  attached  to  whatever  point  is  necessary.     The 
mutual  induction  and  coupling  are  varied  by  moving  the  open  circuit 
helix  as  a  whole.     (Figs.  42  and  43.) 

Making  the  adjustments  to  particular  wave  lengths  and  couplings  is 
called  tuning  and  is  discussed  in  Chapter  VII. 

141.  In  the  latest  Telefunken  sets  (fig.  46)  the  sending  inductance  in 
both  closed  and  open  circuits  consists  of  flat  spirally  wound  coils,  mounted 


MANUAL    OF    WIRELESS    TELEGRAPHY. 


95 


SHOEMAKER 
FIG.   40 


FES3ENPEN 
FIG.  45 


TO  AERIAL 


S 


FESSETNDEN 
FIG.  41       TO  AERIAL 


* 


S 

J 


STONE: 

FIG.  42 

TO  AER/AL 


II     id 

-= 

n   '"  ^ 

(A                 o 

y    § 

MARCONI 

STONE: 

FIG.   43 

INSULATOR 


LOWENSTEIN 

FIG.   47 


TO  AERIAL    J 


iO 

<J 

"I 

^r       H 

>    T               3 

PIERCE 
SLABY  ARCO 

FIG    48 

MASS1E 

FIG.   44 


NOTE. — Figures  40,  41,  42,  44,  and  48  represent  circuits  that  are  not  in 
general  use  to-day,  and  hence  to  the  student  have  a  historical  rather  than  a 
practical  value. 


96  MANUAL    OF    WIRELESS    TELEGRAPHY. 

parallel  and  close  to  each  other  in  a  frame.  Alternate  coils  being  con- 
nected to  a  lever  by  which  their  position  relative  to  the  others  can  be 
varied.  The. coils  are  connected  so  that  currents  in  adjacent  coils  oppose 
each  other  and  decrease  the  self  induction  of  the  whole,  called  by  the 
manufacturers  a  variometer.  By  means  of  the  lever  the  coils  can  be 
separated  and  the  self-induction  and  consequently  the  period  of  the  cir- 
cuit regulated.  This  is  illustrated  in  fig.  46  by  an  arrow  drawn 
diagonally  across  the  inductances  in  which  it  is  used.  Fig.  74  shows  the 
apparatus  as  manufactured. 

142.  For  older  direct  connected  sets  connections  shown  in  figs.  40  and 
44  are  preferred.     The  S  symbol  indicates  alternating  current.     In  the 
figures    referred    to,    the    condenser    is    directly    across    the   secondary 
terminals  of  the  transformer,  and  the  spark  gap  in  one  leg  of  the  closed 
oscillating  circuit,  as  contrasted  with  the  spark  gap  being  placed  directly 
across  the  transformer  terminals.     (Fig.  48.)    The  former  is  considered 
to  be  a  more  symmetrical  arrangement. 

143.  Attention  is  invited  to  fig.  41,  which  shows  one  leg  of  the  trans- 
former directly  grounded  and  the  other  leg  connected  direct  to  the  aerial. 
All  other  methods  of  connection  afford  direct  path  to  ground  and  path 
through  condenser  and  spark  gap.     This  method  of  installation  affords 
path  to  ground  through  condenser  or  spark  gap  only  and  affects  tuning. 
If  the  aerial  is  touched  when  current  is  on  the  transformer,  the  latter, 
having  one  leg  grounded,  is  short-circuited  through  the  body  and  a  severe 
shock  may  be  experienced. 

Though  this  method  of  connection  is  no  longer  used,  it  is  referred  to 
here  to  show  the  necessity  of  giving  careful  consideration  to  the  relative 
positions  of  ground,  spark  gap,  and  condenser.  Errors  in  connections  are 
sometimes  made  so  that  the  most  direct  path  to  ground  is  through  the 
spark  gap.  This  induces  potentials  at  the  gap  or  condenser  approximately 
equal  to  those  at  the  upper  end  of  the  -aerial  and  produces  disagreeable 
inductive  effects  in  the  operating  room. 

144.  Fig.  43  shows  the  preferred  form  of  inductive  connection  or  coup- 
ling, that  is,  one  inductance  above  the  other.     This  takes  up  less  floor 
space  and  the  coupling  is  varied  by  vertical  instead  of  horizontal  move- 
ment, as  is  necessary  when  the  coils  are  side  by  side  as  illustrated  in 
fig.  42. 

Fig.  47  indicates  a  method  of  connecting  up  sending  sets  so  that  the 
operator  by  moving  a  hand  wheel  or  lever  can  change  the  wave  length  of 
the  open  and  closed  circuits  the  same  amount  without  changing  the 
coupling.  This  apparatus  is  just  being  introduced  and  should  greatly 
facilitate  the  operator's  control  over  his  sending  wave  length. 


MANUAL    OF    WIRELESS    TELEGRAPHY.  97 

CAPACITY. 

145.  The  condenser  capacity  necessary  to  absorb  1  K.  W.  at  60  cycles 
and  a  maximum  potential  of  30>000  volts  (A"  gap)  is  .0186  M.  F.  or 
approximately  nine  standard  jars.  (Table  2,  appendix  A.) 

At  500  cycles  and  30,000  volts  it  is  .00223  M.  F.,  a  little  more  than 
one  jar. 

At  500  cycles  and  12,500  volts  (.015  gap)  it  is  .0127  M.  F.,  approxi- 
mately six  jars. 

Older  2  K.  W.  sets  had  capacities  given  below  and  required  maximum 
volts  as  indicated  to  absorb  2  K.  W.  with  two  sparks  per  half  cycle. 

Slaby    Arco,     60  cycle,  capacity    .014  M.  F.,  max.  volt,  app.  35,000,  gap  .5  in.  app. 
Fessenden,  «  «         .004  «  «          65,000,     «  1.6  in.    « 

DeForest, 


.         "  "  .02  "  "          30,000,     "      .5  in.     " 

Shoemaker,  j 

Stone,  «  *»        .0105  "  "          40,000,     "      .6  in.     » 

Sets  now  supplied  have  capacities  based  on  500  cycles  at  12,500  volts, 
condenser  racks  or  tanks  being  arranged  to  hold  a  number  of  jars  some- 
what greater  than  that  necessary  for  the  rated  output. 

146.  For  2  K.  W.  sets  standard  coppered  jars  in  air  or  oil  are  pre- 
ferred.   Tinfoil  covered  jars  are  no  longer  supplied. 

Inside  connections  to  Leyden  jars  are  best  made  by  soldering  one  end 
of  a  strip  of  copper  or  brass  gauze  to  the  inner  copper  coating  and  clamp- 
ing the  other  end  to  the  charging  bus  bar. 

Outside  connections  are  made  either  by  supporting  all  jars  on  a  con- 
ducting plate  connected  to  the  other  charging  bus  bar  or  connecting  this 
bar  to  a  strap  of  sheet  brass  or  copper  clamped  around  the  jar. 

The  important  point  about  condenser  connections  is  that  they  should 
make  a  good  electrical  contact  of  comparatively  large  area,  with  the 
charging  wire  or  bus  bars  and  with  the  condenser  jars  or  plates.  A 
symmetrical  arrangement  of  material  giving  as  nearly  as  possible  equal 
lengths  of  discharge  paths  should  be  made. 

Many  kinds  of  springs  and  clips  for  condenser  connections  have  been 
devised  and  are  in  use,  but  none  are  better  than  those  just  described. 
Less  difficulty  is  experienced  with  connections  on  copper  coated  jars  or 
plates  than  was  the  case  when  tinfoil  was  used  exclusively  for  distributing 
the  charge  over  the  glass  dielectric. 

147.  The  condensers  now  in  use  are  standard  Leyden  jars  in  air  or 
oil.    (Fig.  49.)    Glass  plates  in  air  or  oil  (glass  dielectric).   Metal  plates 
in  compressed  air  (air  dielectric)  (fig.  50)  and  tinfoil  (paper  dielectric). 
For  large  powers,  glass  plates  in  oil  or  metal  plates  in  compressed  air  are 
preferred.    For  small  sets  the  most  convenient  for  use— installation  and 


98 


MANUAL    OF    WIRELESS    TELEGRAPHY. 


FIG.  49. — Ley  den  Jar  Battery. 


FIG.  49A. — Moscicki  Tube.  FIG.  50. — Compressed  Air  Condenser. 


MANUAL   OF   WIRELESS   TELEGRAPHY.  99 

inspection — are  the  standard  jars,  in  air  or  oil,  or  glass  plates  set  ver- 
tically in  oil.  Fig.  49a  is  a  special  form  of  Leyden  jar  which  is  con- 
venient for  some  purposes.  The  low  voltages  associated  with  500  cycle 
sending  sets  have  made  practicable  the  use  of  paper  condensers  as  noted 
above  for  small  powers. 

CONDENSERS  AND  CONDENSER  MATERIAL. 

148.  When  a  piece  of  iron  is  magnetized  and  demagnetized — i.  e.,  goes 
through  a  cycle  of  magnetization — a  certain  amount  of  energy  is  ex- 
pended, which  appears  in  the  shape  of  heat  in  the  iron.  It  is  supposed 
to  be  due  to  internal  friction  in  the  molecules  of  the  iron  and  is  called 
magnetic  hysteresis. 

In  the  same  way,  to  put  a  condenser  through  a  cycle  of  charge  and 
discharge  requires  the  expenditure  of  a  certain  amount  of  energy,  which 
appears  as  heat  in  the  dielectric  and  is  called  dielectric  hysteresis.  The 
loss  of  energy  due  to  this  quality  varies  in  different  dielectrics  and  is  a 
function  of  the  frequency. 

In  choosing  condensers  for  the  closed  sending  circuit,  it  is  of  great 
importance  to  find  those  which  will  absorb  a  minimum  of  energy  and  at 
the  same  time  show  no  tendency  to  break  down  under  the  large  differ- 
ences of  potential  impressed  upon  them. 

The  losses  of  energy  in  condensers  are  of  two  kinds:  internal  losses 
produced  by  dielectric  hysteresis,  and  external  losses  produced  by  the 
brush  discharges  at  the  edges  of  the  conducting  surfaces.  The  ideal 
dielectric  in  respect  to  'the  internal  losses  is  air,  as  it  is  entirely  free  from 
internal  energy  absorption.  When  used  at  ordinary  pressures,  however, 
it  is  unable  to  bear  any  considerable  difference  of  potential.  It  has  been 
discovered  that  when  the  air  pressure  is  increased  to  the  neighborhood  of 
250  pounds,  the  dielectric  strength  becomes  so  great  that  it  is  suitable  for 
use  at  any  of  the  potentials  ordinarily  used  in  wireless  telegraphy. 
Compressed  air  condensers  are  ordinarily  made  up  in  the  form  of  a  series 
of  plates  so  connected  that  the  alternate  plates  may  be  charged  positively 
and  negatively,  and  the  whole  set  is  enclosed  in  an  air-tight  steel  tank 
which  can  be  pumped  up  to  the  desired  pressure.  Such  a  condenser, 
while  ideal  in  its  electrical  properties,  is  somewhat  bulky,  and  difficulties 
are  sometimes  found  in  preventing  leakage  of  the  air.  It  is  therefore 
common  in  stations  where  the  last  degree  of  efficiency  is  not  demanded  to 
make  use  of  glass  condensers,  either  in  the  form  of  flat  plates  or  jars. 
The  conducting  surfaces  of  condensers  are  now  generally  formed  of  elec- 
trolytically  deposited  copper.  It  is  generally  stated  that  flint  glass. is  the 
glass  best  suited  to  form  the  dielectric.  Experiments  which  have  been 
made  show  that  the  internal  losses  of  glass  condensers  in  ordinary  use 
amount  to  from  2  to  8  per  cent  of  the  total  energy  flowing  through  them. 


100  MANUAL    OF    WIRELESS    TELEGRAPHY. 

The  losses  due  to  the  brush  discharges  from  the  edges  of  the  conduct- 
ing surfaces,  which  sometimes  amount  to  30  per  cent  of  the  total  energy, 
may  be  much  reduced  by  immersing  the  condensers  in  oil  or  by  placing 
several  condensers  in  series,  which  reduces  the  individual  potential  differ- 
ence on  each  condenser,  or  by  covering  edges  of  foil  (or  copper)  and 
plates  with  an  insulating  compound. 

149.  Practically  all  other  insulators  have  a  greater  specific  inductive 
capacity  than  air  at  ordinary  pressure,  and  nearly  all  of  them  have  a 
greater  dielectric  strength  than  air  (art.  150).    The  Ley  den  jar,  having 
long  been  used  as  a  high-potential  condenser,  its  method  of  manufacture 
being  well  known,  and  the  best  glass  having  not  less  than  nine  times  the 
capacity  of  air,  has  been  very  generally  used  in  wireless  telegraph  send- 
ing circuits.    Air  and  oil,  while  requiring  much  larger  volume  to  give  the 
same  capacity  as  glass,  have  the  excellent  property  of  mending  themselves 
after  puncture  by  a  spark,  while  all  kinds  of  solid  or  semisolid  dielectrics 
require  renewal  after  rupture. 

Mica  has  very  great  dielectric  strength,  as  much  as  5000  volts  per  mil, 
and  has  been  used  to  some  extent  in  condensers  in  the  form  of  micanite. 

The  semisolid  dielectrics,  such  as  beeswax  and  paraffin,  have  to  be 
made  up  with  considerable  attention  to  the  temperatures  in  which  they 
are  to  be  used,  since  they  may  melt  in  summer  and  crack  in  winter,  but 
they  are  cheap  and  easily  obtained. 

Dielectric  strength  of  insulators  per  millimeter  increases  with  decrease 
of  thickness,  except  in  oils,  where  it  seems  to  decrease. 

Dielectric  strength  of  air  increases  with  increase  of  pressure. 

Dielectric  strength  of  air  decreases  with  decrease  of  pressure  until  the 
pressure  is  in  the  neighborhood  of  1  millimeter  of  mercury^  when  it 
increases. 

Dielectric  strength  of  a  vacuum  should  be  infinitely  great. 

Fleming  states  that  with  the  best  flint  glass  it  is  possible  to  store  about 
45  foot-pounds  of  energy  per  cubic  foot  of  glass.  The  limit  is  set  by  the 
dielectric  strength  of  glass.  He  has  shown  that  the  lengths  of  discharge 
paths  of  all  condenser  elements  should  be  equal. 

Capacity  varies  inversely  and  dielectric  strength  directly,  as  the  thick- 
ness of  the  dielectric,  but  they  do  not  vary  in  the  same  ratio. 

The  dielectric  strength  of  glass  condensers  decreases,  that  of  oil  con- 
densers increases,  with  the  frequency. 

150.  Tables  showing  the  specific  inductive  capacity  of  a  number  of 
dielectrics  and  their  dielectric  strengths  are  given  below.     This  data  is 
incomplete.    Data  relative  to  the  hysteresis  losses  of  various  dielectrics  is 
almost  lacking,  and  want  of  agreement  is  noted  among  different  author- 
ities. 


MANUAL    OF    WIRELESS    TELEGRAPHY. 


101 


Specific 


Material. 


specific 
inductive 
capacity. 


Dielectric 
strength. 

Volt8. 

(  » 4,500 

Air     |  » 3,000 

Hard   rubber    2.29  3  40,000 

India  rubber  2.10  »  30,000 

Mica    6.64  3  60,000 

Micanite 8  40,000 

Typewriter  linen  paper   ...  3  45,000 

Paraffin  oil   2.71  8  7,000 

Glass  (crown)    6.r 

Glass  (plate)    8.45 

Glass   ( light  flint)    6.72  K  '  *  20,000 

Glass  (extra  dense  flint)    9.86 

1  Per  millimeter  for  thicknesses  up  to  1  millimeter.       3  Per  millimeter. 

2  Per  centimeter.        *  4  Approximate. 


102 


MANUAL    OF    WIRELESS    TELEGRAPHY. 


FIG.  51. 


MANUAL    OF    WIRELESS    TELEGRAPHY.  103 

DIELECTRIC  STRENGTH  OF  AIR. 

151.  The  dielectric  strength  of  air  is  considered  to  be  about  4500 
volts  per  millimeter  for  gaps  of  about  1  millimeter  in  length,  and  about 
3000  volts  per  millimeter  for  gaps  of  the  length  of  a  centimeter  or  more. 
Fig.  51  shows  sparking  distances  in  air  between  needle  points,  as  deter- 
mined by  experiment.  These  distances  are  usually  greater  than  those 
obtained  from  equal  voltage  between  the  blunt  spark  points  used  in  wire- 
less telegraphy.  The  latter  probably  correspond  more  closely  to  table 
1,  appendix  A.  On  the  other  hand,  this  table  of  spark  distances  was 
determined  by  raising  the  voltage  very  gradually  and  exactly  alike  for 
each  gap,  while  in  oscillating  circuits  there  is  a  convulsive  rush  which 
may  produce  very  high  potentials.  This  has  been  shown  by  introducing 
a  minute  spark  gap  elsewhere  in  the  circuit,  the  effect  being  to  greatly 
increase  the  gap,  which  can  be  ruptured  by  a  given  transformer  potential. 
The  inertia  of  the  charge  carries  it  forward,  and  just  as  the  inertia  of 
water  in  a  pipe  produces  a  great  pressure  if  its  flow  is  suddenly  checked, 
so  the  potentials  in  the  sending  circuits  may,  and  usually  do,  rise  much 
higher  than  is  indicated  by  the  transformer  ratio. 


104  MANUAL    OF    WIRELESS    TELEGRAPHY.  * 

SPARK  GAPS. 

152.  A  great  deal  of  thought  and  ingenuity  has  been  expended  on 
improving  the  action  of  spark  gaps.  For  instance,  the  use  of  magnetic 
blowouts,  induced  and  forced  air  drafts  across  the  gap ;  dividing  them 
into  a  series  of  short  gaps;  placing  gaps  in  parallel;  enclosing  them  in 
compressed  air  and  in  nitrogen  gas;  making  the  points  hollow  and  cool- 
ing them  with  air  or  water. 

Until  recently,  no  method  of  construction  for  small  powers  was  mark- 
edly better  than  the  ordinary  gap  in  air  between  two  zinc  rods,  J  to  J 
inch  in  diameter,  and  these  are  still  largely  used.  There,  are  two  points 
in  common  for  all  good  working  gaps — (a)  The  sparking  surfaces  must 
be  clean  and  fairly  smooth;  (b)  They  must  be  kept  from  heating. 

The  increased  radiation  from  cooled  spark  electrodes  as  compared  with 
heated  ones  is  very  evident. 

Heated  surfaces  give  off  more  metallic  vapor  and  tend  to  the  forma- 
tion of  a  low  frequency  arc. 

There  is  no  doubt  that  much  of  the  irregularity  noted  in  sending  is  due 
to  an  improperly  adjusted  spark  gap  and  the  effect  known  as  "  soaring  " 
or  "swinging"  is  probably  due  to  the  inequalities  in  the  action  of  the 
spark  gap  and  condensers. 

An  open  spark  must  be  kept  white  and  crackling  and  have  considerable 
volume.    If  too  long,  it  will  be  stringy ;  if  too  short,  an  arc  will  be  formed. 
All  spark  gaps  are  adjustable — either  in  length  or  in  number.     All 
should  be  well  muffled  for  obvious  reasons. 

The  types  of  spark  gaps  now  in  use  are  shown  in  figs.  52-61.  The 
only  types  now  supplied  are  fig.  52,  the  synchronous  rotating  gap,  and 
fig.  57,  quenched  gap. 

153.  The  function  of  the  spark  gap  in  an  oscillatory  circuit  is'to  allow 
the  condenser  to  charge  to  the  required  potential,  and  then  to  break  down 
and  permit  the  charge  to  surge  back  and  forth  until  its  energy  is  dis- 
sipated. The  ideal  spark  gap  would  be  one  which  would  insulate  per- 
fectly while  the  condenser  was  charging  and  conduct  perfectly  while  it 
was  discharging,  and  the  nearer  these  conditions  can  be  fulfilled  the  more 
efficiently  will  the  spark  gap  perform  its  duty.  Either  condition  can  be 
fulfilled  alone,  but  the  combination  is  somewhat  difficult  to  obtain. 

The  resistance  of  the  spark  gap  when  the  discharge  is  passing  depends 
upon  two  factors ;  it  increases  rapidly  with  the  spark  length,  and  de- 
creases rapidly  with  the  oscillatory  current,  amounting  with  a  half-inch 
gap  to  several  hundred  ohms  when  a  fraction  of  an  ampere  passes,  and  a 
small  fraction  of  an  ohm  when  50  or  60  amperes  are  flowing.  With  the 
spark  length  above  half  an  inch,  the  resistance  with  the  same  oscillatory 
current  flowing  may  be  taken  as  roughly  proportional  to  the  spark 
length.  But  in  a  condenser  circuit  the  amount  of  electricity  stored  up  in 


MANUAL    OP    WIRELESS    TELEGRAPHY. 


105 


SPARK     GAPS 


SHAFT   or 
ALTERNATOR 


SYNCHRONOUS    ROTATING  SPARK  GAP          NON-SYNCHRONOUS  ROTATING;  SPARK 
FIG    52  FIG.   53 


FIG     54 


FIG.   55 


X 


AIR  BLAST    QAP 


PARALLEL  QAP 


uc: 

1  . 

Elf 

1 

Vlf 

nx 

\  n\  m 

Jt/O 

m    J 

r~i 

QUENCHED    SPARK    C3AP 
FIG.   57 


FIG.  58      TELEFUNKEN 
(Now  Obsolete) 


MARCONI    DISC    DISCHARGER 

FIG.   56 


FIG.  59       STONE. 
(Now  Obsolete) 


MASSIE    QAP    FOR    COMPRESSEP  AlR  FESSENDEN-J^  FOREST 


FIG.  60 
(Now  Obsolete) 


FIG.  61 
(Now  Obsolete) 


106  MANUAL    OF    WIRELESS    TELEGRAPHY. 

the  condenser,  and  hence  the  amount  of  oscillatory  current,  increases 
with  the  spark  length.  Thus  we  have  two  conditions  working  against 
each  other  as  regards  the  influence  of  the  spark  length  on  the  spark 
resistance;  but  we  can  increase  the  amount  of  current  flowing  without 
increasing  the  spark  length  by  increasing  the  size  of  the  condenser,  and 
the  most  efficient  form  of  circuit  for  a  given  power  is  that  in  which  a 
moderate  spark  length,  and  large  condensers  are  used. 

When,  after  the  condenser  is  charged,  the  spark  gap  breaks  down,  the 
gap  becomes  filled  with  metallic  vapor  and  for  the  time  being  forms  a 
high-frequency  alternating  current  arc.  It  is  the  presence  of  the  metallic 
vapor  which  produces  the  conductivity  of  the  spark.  After  the  discharge 
ceases,  however,  if  this  metallic  vapor  is  not  removed  from  the  gap,  the 
insulation  will  evidently  be  poor  at  the  time  that  the  condenser  is  next 
being  charged,  hence  the  first  condition  of  spark  efficiency  would  be  want- 
ing. It  is  therefore  necessary  to  remove  this  vapor  completely  as  soon  as 
possible  after  the  surgings  of  the  condenser  charge  cease.  This  is  done 
partly  by  cooling  the  electrodes  of  the  spark  gap,  thus  stopping  the 
vaporization,  and  in  some  cases  by  blowing  the  vapors  out  of  the  gap. 

154.  In  the  simple  gap,  such  as  is  found  in  sets  of  small  power,  the 
vapor  is  usuall}7  sufficiently  dissipated  by  the  natural  cooling  of  the 
electrodes  and  by  ordinary  air  currents.     Such  a  gap,  however,  not  pro- 
vided with  an  air  blast  should  not  be  enclosed.     For  somewhat  larger 
powers,  an  air  blast  is  ordinarily  considered  necessary.     This  carries 

'away  the  metallic  vapors  and  at  the  same  time  cools  the  electrodes.   Such 
an  arrangement  is  shown  in  fig.  54. 

Another  form  of  gap  for  small  powers  which  gives  good  satisfaction 
is  the  parallel  gap  (see  fig.  55),  in  which  two  cylinders  of  zinc  or  brass 
are  placed  parallel  to  each  other,  and  the  spark  runs  from  point-  to  point, 
never  jumping  twice  consecutively  in  the  same  place.  This  wandering 
of  the  spark  is  facilitated  by  a  slight  roughening  of  the  electrodes  with 
a  file.  The  explanation  of  this  phenomenon  of  the  running  spark  is 
probably  as  follows:  The  spark  jumps  from  a  slight  projection  on  the 
electrode  which  in  the  course  of  the  oscillations  is  burned  away,  so  that 
at  the  next  discharge  an  easier  path  is  found  from  some  other  projecting 
point. 

155.  For  high  powers  a  good  form  of  spark  gap  is  the  rotating  syn- 
chronous gap  shown  in  fig.  52.    This  consists  of  one  or  more  stationary 
members  and  a  rotating  member  made  up  like  a  wheel  with  projecting 
spokes.     This  in  its  best  form  is  attached  directly  to  the  shaft  of  the 
alternator,  and  is  so  adjusted  that  a  spoke  comes  opposite  a  stationary 
member  at  the  exact  moment  that  the  maximum  of  potential  is  obtained 
in  the  condenser.    This  insures  one  discharge  for  each  alternation  of  the 
current,  the  complete  absence  of  conducting  vapors,  and  gives  a  satisfac- 
tory insulation  for  each  spark.     The  regularity  of  discharge  from  this 


MANUAL    OF    WIRELESS    TELEGRAPHY.  107 

form  of  gap  produces  a  pure  musical  note,  which  is  of  great  importance 
in  the  telephonic  reception  of  signals.     (See  art,  132.) 

156.  Another  form  of  rotating  gap,  called  the  non-synchronous  rotat- 
ing gap,  is  shown  in  fig.  55.    In  this  the  wheel  is  rotated  rapidly  by  an 
independent  motor  without  regard  to  synchronism  with  the  alternator. 
The  face  of  the  stationary  member  of  the  gap  forms  an  arc  of  a  circle 
long  enough  to  a  little  more  than  cover  the  distance  between  two  spokes, 
thus  always  insuring  the  proper  sparking  distance.     The  rotating  wheel 
itself  forms  an  efficient  fan. 

157.  What  is  called  a  "  quenched  gap  "  *  (shown  in  fig.  57)  is  made  up 
of  a  number  of  copper  discs  accurately  turned  and  separated  by  annular 
rings  of  mica  about  .01  inch  thick.     The  spark  is  confined  to  the  air 
tight  space  inside  the  mica-rings. 

This  type  of  gap,  if  a  proper  number  of  discs  are  in  series,  also  gives 
one  discharge  for  each  alternation  of  the  current  and  produces  the  same 
pure  musical  note  as  the  synchronous  gap. 

It  is  almost  noiseless  and  has  the  further  advantage  of  (probably  on 
account  of  its  large  cooling  surface)  quickly  stopping  the  oscillations  of 
the  closed  circuit,  so  that  the  open  circuit  is  left  free  to  vibrate  in  its  own 
period,  and  it  therefore  radiates  waves  of  but  one  length.  This  fact  has 
an  important  bearing  on  the  tuning  of  wireless  telegraph  sets  and  also  on 
the  coupling,  which  can  without  change  of  wave  length  be  made  that 
which  will  transfer  energy  from  the  closed  circuit  to  the  open  circuit 
with  the  least  loss. 

158.  The  quenched  gap  can  not  be  depended  upon  to  operate  without 
artificial  cooling  of  the  discs  when  any  but  very  small  powers  are  used. 
Like  all  other  gaps,  its  action  is  improved  by  an  air  blast. 

In  the  case  of  the  rotating  gap  the  equivalent  air  velocity  in  a  case  of 
large  power  was  about  20,000  feet  per  minute.  Mr.  J.  Martin  finds  a 
very  distinct  gain  in  radiation  from  an  air  cooled  gap  with  air  pressures 
up  to  15  pounds  per  square  inch,  which  corresponds  to  a  velocity  of 
82,000  feet  per  minute,  or  about  1400  feet  per  second. 

Take  a  single  gap  operating  on  a  1000-meter  wave  on  the  peak  of  the 
charging  E.  M.  F. :  If  the  coupling  between  the  open  and  closed  circuits 
is  such  that  the  closed  circuit  transfers  all  its  energy  to  the  open  circuit 
in  five  complete  vibrations  the  first  group  of  sparks  will  last  1/30,000 
second.  To  remove  the  conducting  vapor  from  the  gap  in  that  time  would 
require  a  minimum  air  velocity  across  the  gap  of  1000  feet  per  second  if 
the  electrodes  were  A  inch  (1  cm.)  in  diameter.  From  this  point  of  view 
it  would  seem,  therefore,  that  any  gap  will  act  as  a  quenched  gap  if  the 

*  Discovered  by  N.  Wien,  in  the  course  of  an  investigation  on  electrical 
discharges  between  metal  surfaces  placed  very  close  to  each  other,  and  pub- 
lished by  him  in  October,  1906. 

8 


108  MANUAL   OF   WIRELESS   TELEGRAPHY. 

air  velocity  across  the  gap  is  sufficiently  great,  and  that  the  required  air 
velocity  varies  directly  as  the  diameter  of  the  spark  electrodes — inversely 
as  the  wave  length,  directly  as  the  damping — and  (since  it  is  known  that 
close  coupling  increases  the  damping)  directly  as  the  percentage  of 
coupling. 

Loose  coupled  circuits  would  require  a  lower  air  velocity  than  close 
coupled  ones. 

Fig.  56  illustrates  the  Marconi  disc  discharger,  which  is  practically 
the  same  in  principle  as  fig.  53 — the  non-synchronous  rotating  gap.  A 
special  motor  is  required  to  operate  the  discharger.  It  has  also  the  dis- 
advantage of  being  as  noisy  as  the  synchronous  gap.  The  disc  discharger, 
like  the  synchronous  rotating  gap,  is  suitable  for  large  powers.  It  is 
fitted  with  an  auxiliary  stationary  gap  for  use  in  case  of  motor  break- 
down. 

TRANSFER   OF   ENERGY  BETWEEN   COUPLED  CIRCUITS. 

159.  The  transfer  of  energy  between  coupled  circuits  having  the  same 
natural  period  is  well  illustrated  by  the  mutual  action  of  two  similar 
pendulums  connected  by  a  flexible  support.     If,  one  being  at  rest,  the 
other  is  pulled  aside  and  released,  the  swinging  pendulum  gives  properly 
timed  impulses  to  the  other  through  the  flexible  connection  and  starts 
it  to  swinging  also,  gradually  decreasing  its  own  swings  while  the  other 
increases,  until  the  first  one  stops ;  at  which  time  the  second  has  reached 
an  amplitude  nearly  as  great  as  that  of  the  first  swing  of  the  one  pulled 
aside.     In  other  words,  all  of  the  energy  has  been  transferred  to  the 
second  pendulum.     The  first  one  then  starts  again  and  increases   its 
swings  while  the  second  gradually  slows  down  and  comes  to  rest  at  which 
time  the  first  is  again  at  its  maximum.    All  the  energy  has  been  returned 
by  the  second  pendulum  to  the  first.     The  swings  are  slowly  damped 
by  air  friction  until  the  system  comes  to  rest.    If  the  periods  of  the  two 
pendulums  are  not  equal,  or  nearly  so,  the  impulses  are  out  of  step 
(resonance)   and  no  transfer  of  energy  takes  place — the  pendulum  first 
started  keeps  on  swinging  and  the  second  remains  at  rest. 

160.  If  the  points  of  support  by  the  flexible  connection  are  a  foot  or 
more  apart  (loose  coupling)   the  second  pendulum  picks  up  the  swing 
rather  slowly  and  both  pendulums  make  a  large  number  of  vibrations 
before  the  second  has  received  all  the  energy  from  the  first  and  the 
latter  has  come  to  rest. 

If  thet points  of  support  are  close  together  (close  coupling)  the  second 
pendulum  reaches  its  maximum  and  the  first  comes  to  rest  in  a  few  vibra- 
tions, the  transfer  of  energy  is  more  rapid,  and  the  damping  greater. 
The  ball  of  energy,  so  to  speak,  is  tossed  back  and  forth  between  them 
more  rapidly  than  when  they  are  farther  apart — more  loosely  coupled. 


MANUAL    OF    WIRELESS    TELEGRAPHY.  109 

Professor  Pierce  *  has  photographed  the  sparks  in  a  short  gap  in  the 
open  circuit  when  oscillating  in  connection  with  the  closed  circuit  and 
shows  that  they  occur  in  groups.  This  particular  circuit  showed  groups 
of  four.  In  other  words,  four  vibrations  sufficed  to  transfer  all  the 
energy  from  one  circuit  to  the  other. 

Two  circuits  may  be  alike  in  period,  but  have  different  dampings. 

161.  Eeturning  now  to  the  consideration  of  the  quenched  gap  and  the 
closed  circuit,  what  we  call  the  closed  circuit  is  only  closed  when  the 
spark  gap  is  conducting  and  its  period  in  that  condition  is  the  one 
measured  either  when  we  take  the  time  interval  between  sparks  or  deter- 
mine it  by  a  wave  meter.    It  has  a  different  period  when  the  spark  gap 
is  not  conducting  because  its  capacity  with  reference  to  being  charged 
from  the  open  circuit  is  less  and  it  is  therefore  out  of  tune  with  the  open 
circuit  and  the  latter  does  not  transfer  any  energy  to  it.    The  effect  of  the 
method  of  construction  of  the  quenched  gap  seems  to  be  to  restore  the 
nonconducting  character  of  the  gap  the  first  time  the  closed  circuit  comes 
to  rest,  and  thus  leave  the  open  circuit  free  to  radiate.    It  would  be  inter- 
esting to  take  photographs  in  both  circuits  to  determine  whether  this 
really  is  the  case. 

162.  Eeferring  to  art.  109  on  mutual  induction:    The  open  circuit  is 
first  set  to  oscillating  in  either  the  period  longer  or  shorter'  than  its 
natural  period  and  has  reached  its  maximum  when  the  closed  circuit  has 
stopped  and  opened.    Thereafter  the  open  circuit  is  free  to  vibrate  in  its 
own  period,  and  that  it  changes  to  that  period  is  shown  by  the  wave  meter 
readings,  but  in  building  up  it  is  sending  out  waves  of  a  different  period. 

The  first  maximum  reached  in  the  open  circuit  is  the  highest  maximum 
and,  since  no  further  loss  by  re  transfer  to  the  closed  circuit  takes  place, 
the  quenched  gap  is  consequently  the  most  efficient.  It  will  also  con- 
duce to  efficiency  to  make  the  building  up  period  of  the  aerial  (when  it 
is  radiating  waves  of  a  different  length)  as  short  as  possible.  In  other 
words,  close  coupling,  but  close  coupling  increases  the  induced  E.  M.  F. 
in  the  condenser  circuit.  Therefore,  there  is  a  possibility  with  very  close 
coupling  of  retransfer  of  energy  by  breaking  down  the  gap  and  again 
closing  that  circuit. 

163.  We  can,  therefore,  conceive  of  a  wave  train  from  an  ordinary  open 
circuit  as  made  up  of  a  series  of  waves  whose  amplitude  rises  and  falls 
during  the  transfer  and  retransfer  of  energy  from  one  circuit  to  the 
other;  the  damping  depending  on  the  coupling  and  being  partly  natural 
(due  to  heating  and  radiated  energy  in  the  shape  of  electric  waves), 
partly  artificial  (due  to  retransfer  of  energy  to  the  closed  circuit). 

*  G.  W.  Pierce,  Principles  of  Wireless  Telegraphy,  1910,  p.  248. 


110 


MANUAL   OF    WIRELESS    TELEGRAPHY. 


A  wave  train  from  the  open  circuit  of  a  quenched  gap  can  be  repre- 
sented, as  in  fig.  62,  by  a  building  up  at  a  certain  frequency  (depending 
on  the  coupling)  to  a  maximum  depending  on  the  radiation  or  other 
losses  per  oscillation,  and  then  oscillations  in  the  natural  period  of  the 
open  circuit,  with  damping  dependent  on  the  radiation  and  resistance  of 
the  open  circuit  only.  The  closed  circuit  starting  at  a  maximum  and 
transferring  all  the  energy  to  the  open  circuit  in  a  few'  oscillations  as 
shown  in  the  upper  part  of  fig.  62 ;  there  being  no  retransfer  of  energy 
from  the  open  to  the  closed  circuit  and  vice  versa  as  occurs  with  the 
pendulums  discussed  in  arts.  159  and  160. 


Closed 


. 


Open 


SPARK 


FIG.  62. 


164.  The  results  of  experiments  indicate  that  the  decrement  of  the 
open  circuit  which  will  give  good  tuning  must  be  not  greater  than  .2  per 
oscillation,  and  this  is  represented  in  fig.  62.  This  rate  of  decrease  of 
amplitude  gives  about  fifteen  complete  vibrations  before  the  amplitude 
falls  to  one-tenth  of  the  maximum. 

The  above  gives  as  the  length  of  a  425-meter  wave  train  from  a  500- 
cycle  generator  about  3.3  sea  miles,  its  duration  1/47,000  second,  the 
distance  between  wave  trains  186  miles,  the  time  interval  1/1000  second, 
so  that  even  with  a  frequency  of  500  cycles  we  only  generate  electric 
waves  about  2$  of  the  time. 


MANUAL   OF   WIRELESS   TELEGRAPHY.  Ill 

LIMITATIONS   ON   WAVE  LENGTHS. 

165.  A  certain  amount  of  inductance  is  necessary  in  the  closed  circuit 
in  order  to  transfer  energy  to  the  open  circuit,  whether  the  circuits  are 
direct  or  inductively  coupled.  Since  condensers  of  any  desired  capacity 
can  readily  be  obtained,  it  is  easy  to  make  the  closed  circuit  any  electrical 
length  we  desire. 

There  is,  however,  a  lower  limit  to  this,  depending  on  the  material  and 
arrangement  of  the  condenser  and  leads.  Other  things  being  equal,  the 
larger  the  capacity,  the  longer  the  connecting  leads;  and  the  shortest 
wave  length  that  can  be  obtained  for  a  given  capacity  is  that  found  when 
the  leads  from  the  condenser  are  connected  in  the  most  direct  manner  to 
those  from  the  closed  circuit  and  spark  gap. 

The  standard  wave  length  for  ships  and  shore  stations  was  first  set 
at  320  meters.  It  is  now  600-1000  meters  for  ships.  It  will  be  noted 
that  the  increase  in  frequency  to  500  cycles  will,  though  the  standard 
voltage  has  been  lowered,  permit  a  decrease  of  capacity  and  thus  permit 
the  radiation  of  larger  powers  on  shorter  wave  lengths  than  is  now 
practicable. 

Experience  shows  that  aerials  with  short  wave  lengths  radiate  more 
efficiently  than  those  with  long  ones,  and  that  up  to  several  hundred 
miles  short  waves  travel  over  salt  water  with  no  great  absorption;  when 
transmission  over  land  is  necessary  and  for  long  distances  over  water 
we  gain  more  by  the  reduced  absorption  of  long  waves  than  we  lose  by 
decreased  radiation  efficiency. 

166.  The  open  circuit,  while  it  has  concentrated  inductance  like  the 
closed  circuit,  has  distributed  capacity  which  is  comparatively  small,  and 
though  any  electrical  length  we  desire  can  be  obtained  by  adding  induc- 
tance, it  is  found  that  concentrated  inductance  beyond  that  necessary  to 
receive  energy  from  the  closed  circuit  lessens  the  radiation,  and  on  that 
account  it  is  necessary  to  increase  the  period  of  the  open  circuit  by  adding 
capacity  in  the  shape  of  additional  wires  to  the  aerial.  We  have  seen 
that,  unless  they  are  quite  a  distance  apart,  two  parallel  wires  do  not  have 
twice  the  capacity  of  one,  so  that  it  is  practically  difficult  to  get  very  long 
wave  lengths  in  the  open  circuit,  especially  on  shipboard. 

The  wave  lengths  that  we  can  efficiently  use  in  the  open  circuit  are, 
therefore,  limited  by  practical  considerations. 

Since  the  energy  in  any  discharge  varies  as  the  square  of  the  voltage, 
and  since  any  desired  voltage  can  readily  be  obtained,  the  work  that  can 
be  stored  in  a  condenser  of  given  capacity  depends  only  on  the  dielectric 
strength  of  the  condenser  material. 

But  in  the  case  of  the  open  circuit,  when  the  first  transfer  of  energy  is 
completed,  unless  it  is  radiated  nearly  as  fast  as  received,  the  maximum 


112  MANUAL    OF    WIRELESS    TELEGRAPHY. 

voltage  in  the  open  circuit,  on  account  of  its  capacity  being  very  much 
smaller,  is  much  greater  than  that  in  the  closed  circuit.  And  we  find 
that  very  high  voltages,  on  account  of  difficulty  of  insulation,  break  out 
in  sparks  at  all  points  of  the  circuit,  that  the  aerial  wire  glows  through- 
out its  length,  and  the  whole  apparatus  generally  acts  like  a  dry  linen 
fire  hose  when  subjected  to  a  high  water  pressure — i.  e.,  it  spurts 
electricity  at  all  points  in  all  directions. 

So  practical  considerations  limit  the  wave  lengths  that  can  be  efficiently 
used  on  board  ship,  and  also  limit  the  power  that  can  be  used  with  them. 

167.  Eef erring  to  the  closed  circuit,  it  is  probable  that  the  best  results 
with  any  given  sender  are  obtained  when  the  work  necessary  to  charge 
the   condenser   to   the   transformer   voltage    is   equal   to   that   supplied 
by  the   available  power   of  one-half   alternation.     This   gives   but   one 
wave  train  per  alternation,  and,  if  true,  fixes  at  once  the  capacity  of 
the  closed  sending  circuits  for  any  given  power.     Good  results,  how- 
ever, have  been  obtained  by  producing  a  condition  of  resonance  in  the 
secondary  circuit  with  the  primary  frequency  and  obtaining  a  wave  train 
only  every  two  or  more  alternations. 

However,  if  the  generator,  sending  circuits  and  aerial  are  properly 
designed,  the  greater  power  per  wave  train  will  be  gained  at  the  expense 
of  efficiency  on  account  of  the  high  voltages  in  the  aerial  and  the  reduced 
spark  frequency. 

OPEN  CIRCUIT — (AERIAL,  INDUCTANCE,  GROUND). 

168.  Aerials,  with  which  the  open  circuit  inductances  of  sending  sets 
are  connected,  are  shown  diagrammatically  in  figs.  63  to  71  inclusive. 

The  main  principles  to  be  remembered  in  connection  with  aerials  (or 
antennas,  as  they  are  sometimes  called)  are  that  the  higher  the  aerial  the 
more  efficiently  the  energy  will  be  radiated  in  the  form  of  electric  waves 
and  the  larger  the  currents  induced  in  the  vertical  part  of  the  aerial  the 
greater  the  amount  of  energy  radiated. 

So  what  we  need  is  height  for  efficiency;  and  capacity  for  amount  (dis- 
tance). The  former  is  limited  by  the  height  of  mast;  capacity  by  the 
amount  of  wire  that  we  can  conveniently  support  at  the  mast  heads. 
Experiment  indicates  that  distance  for  the  same  power  and  received  on 
the  same  antenna  varies  as  the  height  up  to  100-200  miles. 

The  total  capacity  of  a  ship  aerial  is  usually 'less  than  one  standard  jar. 
To  hold  the  same  amount  of  energy  as  the  condenser  circuit  the  aerial 
is,  therefore,  while  oscillating,  charged  to  a  higher  maximum  potential. 
The  form  of  aerial  now  generally  used  on  ships  and  ashore  is  called  the 
flat-top  or  inverted  L  (fig.  67). 

The  leads  to  the  operating  room  are  taken  from  one  end;  the  other 
(free)  end  is  subject  to  high  potentials  and  must  be  well  insulated. 


MANUAL    OF    WIRELESS    TELEGRAPHY. 


113 


FIG.   63    BELLINI-TOSI 


FIG.   64  MARCONI 


GUYS 


(SUY9 


•MAST 

FIG.   65     UMBRELLA 


STONE: 


MASSIEL 


f  TO  SENDlNq 
FIG.   67 


INSULATED  WIRE     *    BARE  W)f?ET 

FIG.   66 
(Now  Obsolete) 


TO  SENPING*  HELIX. 


FIG.   68 
(Now  Obsolete) 


TO  SEMpINQ  HELIX 
FIG.    69 

(Now  Obsolete) 


HELIX 


4  TO  SENDING  HELIX 
FIG.   71 


114  MANUAL    OF    WIRELESS    TELEGRAPHY. 

Some  T  aerials  are  in  use  (fig.  70).  They  give  greater  relative  capacity 
for  the  same  amount  of  wire,  but  as  we  shall'  see  presently,  the  natural 
period  of  the  flat  top  is  not  too  great.  T  aerials  sag  in  the  center,  thus 
decreasing  their  effective  height  and  they  are  subject  to  high  potentials 
at  both  ends. 

The  other  types  shown  are,  or  have  been,  used  on  shore  stations,  except 
the  special  receiving  aerial  shown  in  fig.  63,  which  is  a  direction  aerial 
used  on  ships  and  which  will  be  referred  to  in  Chapter  VIII. 

The  umbrella  aerial  shown  in  fig.  65  has  been  used  at  some  large 
shore  stations.  It  is  probably  the  best  form  that  can  be  supported  by  a 
single  mast. 


FIG.  72. — Wireless  Telegraph  Anchor  Spark  Gap. 
LOOPED  AERIALS. 

169.  It  will  be  noted  that  the  diagrams  of  receiving  sets  (figs.  82  and 
83)  show  an  aerial  in  the  form  of  a  loop,  beyond  three  spark  points 
arranged  in  the  form  of  a  triangle.  The  lower  one  of  these  points  is  con- 
nected to  the  sending  circuit  inductance  so  that  as  far  as  sending  is 
concerned  this  aerial  is  the  same  as  any  other,  since  the  high  potentials 
used  in  sending  easily  jump  the  short  gaps  between  the  two  sides  of  the 
loop;  but  for  receiving  it  is  different — the  weak  currents  can  not  jump 
the  gap,  which  is  known  as  an  anchor  spark  gap,  so  that  the  circuit  is 
only  looped  for  receiving  and  not  sending. 


MANUAL   OF    WIRELESS   TELEGRAPHY.  115 

The  anchor  spark  gap  (fig.  72)  serves  to  cut  out  the  sending  circuit 
when  receiving.  When  sending,  the  volume  and  color  of  the  sparks  in  the 
anchor  gap  serve  to  indicate  roughly  whether  the  sending  apparatus  is 
working  properly.  For  receiving  sets  not  requiring  a  looped  circuit  the 
two  sides  of  the  loop  are  joined  below  the  gap  and  used  as, a  single  wire. 
A  little  consideration  will  show  that  the  wave  length  of  a  loop  is  the  same 
as  that  of  half  the  loop  on  open  circuit.  A  loop  is,  however,  a  persistent 
oscillator. 

170.  Except  where  they  pass  near  conducting  objects  or  through  decks, 
all  parts  of  the  aerial  wire  are  left  bare  on  account  of  the  lighter  weight 
and  smaller  surfaces  exposed  to  the  wind  as  compared  with  insulated 
wire.     The  size  of  wire  generally  used  is  made  up  of  seven  strands  of 
No.  20  B.  &  S.  phosphor  or  silicon  bronze  wire  or  monnot  metal  having 
fairly  high  elastic  strength. 

Stranded  wire  is  more  flexible,  and  the  materials  given  above  have 
fairly  good  conductivity  and  much  greater  elasticity  than  copper  wire. 
The  elasticity  prevents  permanent  elongation  and  sagging  after  being 
hauled  taut. 

171.  The  natural  wave  lengths  of  certain  aerials  of  the  flat  top  type 
(inverted  L  and  T  aerials,  figs.  67  and  70)  are  given  in  tabular  form 
below.     To  the  aerial  is  added  the  necessary  turns  on  the  open  circuit 
helix  to  bring  the  natural  wave  length  to  425  meters.    It  usually  requires 
a  number  of  turns  of  the  helix  to  do  this.    When  it  is  desired  to  greatly 
increase  the  sending  wave  length  special  loading  coils  are  added  to  the 
open  circuit.    (See  figs.  45,  46  and  47.)    Since  the  closed  circuit  has  large 
capacity  and  small  self-induction  a  turn  or  more  of  inductance  added  to 
the  closed  circuit  makes  a  large  percentage  addition  to  its  self-induction 
and,  therefore,  to  its  wave  length.    But  the  open  circuit  has  small  capacity 
and  relatively  large  self-induction,  so  that  each  additional  turn  does  not 
make  such  a  large  percentage  addition  to  its  self-induction  and,  therefore, 
its  increase  of  wave  length  per  additional  turn  is  much  less  than  that 
of  the  closed  circuit.     (See  Adjustments,  Chapter  VII.) 


116 


MANUAL    OF    WIRELESS    TELEGRAPHY. 


Ship. 

Type. 

No. 
wires. 

Distance 
apart. 

Length  of 
flat  top. 

Vertical 
length  of 
lead  to 
operating 
room. 

Total 
length. 

Natural 
wave 

(meters). 

Glacier 

T 
T 
T 
T 
1 
1 
T 
1 

i 

Inverte 
pyrami 

10 
8 
6 
6 
8 
4 
4 
4 
4 
d 

2  feet 
26  inches 
2  feet 

3    " 

4  feet 
4    " 
5     " 
4    " 

170  feet 

124    " 
140    " 
150    " 
160    " 
160    " 
125    " 
120    " 
130    " 

82  feet 
132    " 

136    " 
129    " 
97    " 
90    " 
137    " 
120    " 
132    " 
200    " 

252  feet 
256    " 
276    " 
279    " 
257    " 
250    " 
262    " 
240    " 
262    " 

330 
360 
330 
425 
395 
385 
360 
330 
370 
900 

Mayflower 

Dolphin 

Louisiana  .         ... 

Chester  

Birmingham  

Connecticut  

Maine  

Baltimore 

Guantanamo  

a. 

172.  In  all  aerials  referred  to  above,  except  the  Maine  and  Baltimore, 
the  long  wave  contained  the  greater  amount  of  energy.  In  the  case  of 
these  two  aerials  the  greater  amount  of  energy  was  radiated  on  the  short 
wave. 

These  sets  (except  the  Shoemaker,  whose  closed  circuit  was  designed 
to  give  loose  direct  coupling  at  425  meters,  and  which  did  not  require  the 
use  of  the  aerial  loading  coil  for  4-25  meters)  had  no  direct  provision  for 
changing  the  wave  length  of  the  aerial  except  in  the  coupling  coil,  and, 
therefore,  when  coupled  gave  a  wider  variation  from  the  standard  wave 
length  than  the  Shoemaker  sets. 


OPEN  CIRCUIT  INDUCTANCE. 

173.  With  direct  coupling  the  open  circuit  inductance  forms  part  of 
the  same  helix  as  the  closed  circuit  inductance,  as  has  already  been 
stated.     (See  fig.  40.)     In  inductively  coupled  sets  the  open  circuit  helix 
is  movable,  so  that  the  coupling  can  be  varied  by  moving  the  entire 
coil  while  keeping  the  same  wave  length.     Provision  is  also  made  for  a 
variable  connection  to  the  helix  so  that  the  wave  length  can  be  varied. 
(Figs.  42  and  43.) 

174.  It  must  not  be  forgotten  that  varying  the  wave  length  of  either 
circuit  by  varying  the  inductance  of  the  coupling  coil  or  coils  varies  the 
mutual  induction,  as  well  as  the  self-induction,  and  also  the  coupling 
and  damping,  so  that  the  most  recent  sets — Fessenden  (fig.  45),  Tele- 
funken  (fig.  46),  Lowenstein  (fig.  47) — make  provision  for  varying  the 
wave  length  at  some  other  part  of  the  circuit  than  at  the  coupling  coil, 
or,  as  in  the  Lowenstein  sets,  for  automatically  moving  the  coils  so  as  to 
maintain  the  same  coupling  when  the  wave  length  is  varied.   These  out- 


MANUAL   OF   WIRELESS   TELEGRAPHY. 


117 


side  coils  are  called  loading  coils,  as  distinguished  from  the  coupling 
coils.,  by  means  of  which  energy  is  transferred  from  the  closed  to  the 
open  circuit  (and  vice  versa  in  sets  not  having  quenched  or  properly  air- 
cooled  gaps). 


• 


FIG.  73.— Helix  and  Spark  Gap. 


The  method  of  building  the  Telefunken  variometer  coils,  shown  in 
fig.  46,  is  illustrated  further  in  fig.  74.  This  method  of  varying  the 
self-induction  of  a  circuit  has  the  advantage  of  not  having  any  dead  ends 
as  in  the  old  inductance  helices,  shown  in  fig.  73.  However,  the  vari- 
ometer shown  in  fig.  74  is  not  suitable  for  inductive  coupling. 

None  of  the  sending  sets  now  in  use  permit  the  wave  length  of  both 
open  and  closed  circuits  to  be  changed  without  some  effort  and  more  than 
one  movement  of  the  operator. 

Additional  remarks  on  coupling  will  be  found  under  "  Adjustments," 
Chapter  VII. 

For  those  parts  of  the  aerial  which  require  insulation  to  protect  it  from 
grounding  and  to  protect  persons,  a  special,  heavily  insulated  wire  called 
rat-tail  wire,  is  used. 


118 


MANUAL    OF    WIRELESS    TELEGRAPHY. 


A  lightning  switch  (fig.  75)  is  installed  outside  the  station,  or  where 
the  aerial  enters,  by  means  of  which  it  is  grounded  during  thunder 
storms. 

The  other  aerial  accessory — the  hot  wire  ammeter  (fig.  76)— r-is  in- 
stalled in  the  ground  lead;  its  uses  are  particularly  referred  to  in 
Chapter  VII. 


FIG.  74. 


GROUNDS  AND  GROUND   CONNECTIONS. 

175.  As  has  been  previously  explained,  wireless  telegraphy  makes  use 
of  earthed  electric  waves,  as  compared  with  the  free  waves  discovered  by 
Hertz  and  used  by  Marconi  in  his  first  experiments.  It  was  soon  found 
by  Marconi  that  good  connection  to  earth  or  to  a  large  conducting  body 
is  essential  to  good  working.  On  board  ship  the  end  of  the  aerial  below 
the  open  circuit  inductance  (called  the  ground  lead)  must  be  well 
soldered,  bolted,  or  clamped  to  some  portion  of  the  hull. 

A  grounded  vertical  wire  well  earthed  has  a  wave  length  not  less  than 
four  times  its  natural  length.  At  its  free  end  there  is  a  potential  loop 
and  a  current  node  (maximum  potential — no  current).  At  its  earthed 
end  there  is  a  current  loop  and  potential  node  (maximum  current — no 
potential).  (See  fig.  18d.)  The  same  wire  free  at  both  ends  has  an 
electrical  period  equal  to  twice  its  length,  and,  if  oscillating,  has  high 


MANUAL    OF    WIRELESS    TELEGRAPHY. 


119 


potentials  at  both  ends.  If  the  ground  connection  is  not  good,  there  is  a 
tendency  to  choke  the  current  passing  in  and  out  of  the  earth  and  thus 
to  cause  a  rise  of  potential  and  consequent  sparking  and  reflection  of 
energy  at  the  earth  connections,  making  the  period  irregular  and  impair- 
ing the  sending  qualities  of  the  station. 


FIG.  75. — Lightning  Switch. 


FIG.  76. — Hot  Wire  Ammeter. 


It  should  be  possible  to  grasp  the  ground  lead  where  it  is  soldered  to 
the  ship  without  injury.  Inability  to  draw  a  spark  there  is  proof  of 
good  connection. 

176.  At  shore  stations  it  is  found  that  the  resistance  of  the  earth  be- 
tween two  earthed  conductors  a  given  distance  apart  varies  widely  in 
different  localities  and  in  the  same  locality  with  moisture  and  tempera- 
ture, and  low  ground  resistance  at  a  station  is  usually  accompanied  by 
good  radiating  qualities.  Where  and  when  the  soil  is  very  dry  it  is  neces- 
sary to  pay  much  greater  attention  to  the  area  of  the  ground  connections, 


120  MANUAL    OF    WIRELESS    TELEGRAPHY. 

and  where  the  resistance  of  the  earth  in  the  vicinity  of  the  station  is  high 
the  station  is  a  poor  radiator  unless  an  artificial  ground  called  a 
"  counterpoise  "  is  installed.  This  can  consist  of  any  large  conducting 
area  laid  on  the  ground  or  wires  connected  between  the  mast  guys.  The 
natural  period  of  the  counterpoise  should  be  the  same  as  that  of  the 
aerial. 

Generally  a  good  ground  is  made  by  connecting  the  ground  lead  to 
copper  plates  of  large  area  in  good  contact  with  moist  earth,  or  to 
radiating  lines  of  galvanized  iron  telegraph  wire  ending  in  pipes  driven 
to  moist  earth,  or  to  wire  netting  spread  on  the  ground  and  covered  with 
earth.  At  stations  on  tops  of  buildings  grounds  are  made  to  the  steel 
frames  of  the  building  and  to  water  and  gas  pipes. 


Chapter  VI. 

RECEIVING  CIRCUITS  AND  APPAEATUS. 

177.  Receiving  circuits  will  be  considered  in  the  following  order,  viz.: 
Open  circuit,  closed  circuit,  condensers,  inductances,  detectors,  telephones, 
batteries,  ampliphones,  recorders. 

In  practically  all  cases  the  same  aerial  wire  is  used  for  both  sending 
and  receiving. 

The  advancing  waves  of  electric  and  magnetic  force  from  the  sending 
aerial  cut  the  receiving  aerial  and  induce  in  it  oscillating  currents.  If 
the  receiving  circuit  has  the  same  period  as  that  of  the  passing  waves,  the 
induced  oscillating  currents  in  the  aerial  will  increase  until  the  energy 
dissipated  per  oscillation,  by  re-radiation,  resistance,  and  transfer  to  other 
parts  of  the  receiving  circuit,  is  equal  to  that  received  per  wave. 

If  the  receiving  aerial  circuit  is  directly  or  inductively  connected  to  a 
closed  oscillating  circuit  to  which  part  of  the  energy  received  per  wave  is 
transferred  during  each  oscillation  instead  of  being  re-radiated,  this 
closed  oscillating  circuit  will  absorb  energy,  and  if  its  period  is  equal  to 
that  of  the  arriving  waves  the  oscillations  will  increase  in  amplitude  with 
each  half  period  since  a  closed  circuit  radiates  slowly.  If  a  detector  is 
placed  in  either  the  open  or  closed  circuit  so  that  the  oscillating  currents 
produce  differences  of  potential  at  its  terminals  and  the  maximum  ampli- 
tude of  the  oscillation  set  up  is  sufficient  to  make  it  function,  the  passing 
of  groups  of  wave  trains  separated  into  dots  and  dashes  at  the  sending 
station  can  be  detected  at  the  receiving  station. 

At  the  sending  station  the  closed  circuit  furnishes  energy  to  the 
radiating  circuit,  which  sends  it  out  in  the  shape  of  electric  waves. 

At  the  receiving  station  this  radiating  circuit  absorbs  energy  from 
the  passing  wraves  and  transfers  to  the  closed  circuit  part  of  what  it 
absorbs. 

It  is  evident  that  no  spark  gap  is  required  in  the  closed  receiving  cir- 
cuit and  that,  since  no  high  potentials  nor  heavy  currents  need  be 
provided  for,  it  is  not  necessary  that  the  receiving  inductances  and 
condensers  should  have  the  same  dimensions  or  arrangement  as  those  in 
the  sending  circuits.  But  in  all  other  features  receiving  circuits  are  the 
exact  analogue  of  sending  circuits  and  the  detector  could  occupy  the 
place  of  the  spark  gap.  However,  all  detectors  consume  energy,  and 
placing  them  either  directly  in  series  with  the  aerial  or  in  the  closed 
receiving  circuit  is  equivalent  to  placing  a  certain  amount  of  resistance 
in  series  with  these  circuits,  and  therefore  increases  the  resistance  and 


122 


MANUAL   OF   WIRELESS   TELEGRAPHY. 


ELEMENTARY  DIAGRAMS,  RECEIVING,  AND  DETECTOR  CIRCUITS. 


<XXXXP^ 


FIG.  77 
(Now  Obsolete) 

MASSIC 


8 


FIG.  78 
(Now  Obsolete) 


DE  FOREST 


FIG.  81 
(Now  Obsolete) 


SHOEMAKER 


FIG.   82  "* 
(Now  Obsolete) 


i 


FIG.   83 


MANUAL    OF    WIRELESS    TELEGRAPHY.  123 

hence  the  damping  and  interferes  with  the  building  up  of  the  induced 
current  and  the  tuning  of  the  circuit. 

It  is  found  by  experiment  that  the  strongest  signals  are  obtained  when 
a  certain  fraction  of  the  total  energy  is  taken  up  by  the  detector.  It  is 
usually  placed  in  the  closed  circuit  or  in  shunt  across  the  terminals  of 
the  closed  circuit  condenser.  When  placed  directly  in  the  aerial,  it  is 
only  suitable  for  receiving  a  highly  damped  wave  train — one  in  which 
nearly  all  the  energy  is  contained  in  the  first  oscillation. 

178.  Keceiving  and  detector  circuits  are  illustrated  in  figs.  77  to  88 
inclusive. 

In  all  figures,  the  fixed  condensers  shown  are  for  the  purpose  of  pre- 
venting the  direct  current  from  the  battery  or  detector  from  flowing 
through  the  inductance.  Variable  condensers,  and  variable  inductances 
are  used  for  changing  the  period  (wave  length)  of  the  circuits. 

Eeferring  to  fig.  79,  the  cup-shaped  construction  under  the  word 
Fessenden  indicates  a  detector.  The  construction  shown  above  the  figures 
79  indicates  a  telephone  in  all  diagrams.  The  non-inductance  resistance, 
with  arrow-headed  connection,  is  used  to  regulate  the  impressed  voltage 
at  the  detector  terminals.  It  is  called  a  potentiometer.  Other  symbols 
used  have  been  previously  described. 

Fig.  77  shows  the  detector  (in  this  case  a  coherer — see  art.  188)  in 
shunt  in  the  open  circuit,  the  open  circuit  having  a  variable  tuning 
inductance.  The  remainder  of  the  figure  shows  the  coherer-tapper,  call, 
and  the  relay  for  the  Morse  recorder. 

Fig.  77,  like  figs.  78  and  79,  illustrates  direct-connected  receiving  sets. 
They  are  not  now  generally  used.  Inductively  connected  sets,  shown  in 
figs.  80,  83,  85  and  86,  are  preferred. 

It  will  be  noted  that  in  fig.  83  provision  is  made  for  tuning  the  closed 
circuit  with  detector  directly  in  circuit;  while  in  the  Fessenden  interfer- 
ence preventer  illustrated  in  fig.  85,  no  provision  is  made  for  tuning  the 
detector  circuit. 

In  figs.  80  and  86  the  detector  is  in  shunt  around  a  closed  tuned  circuit. 

In  all  inductively  connected  receiving  sets  provision  is  made  for  vary- 
ing the  mutual  induction  between  the  open  and  closed  circuits.  (See 
art.  182.)  This  whether  the  closed  circuit  is  tuned  or  untuned. 

Dr.  Austin  states  that  the  only  advantage  of  tuning  the  detector 
circuit  is  a  slight  increase  in  selectivity  and  that  no  louder  signals  are 
produced.  Professor  Pierce's  investigations  of  detector  circuits,  like  those 
in  fig.  83  (except  that  the  closed  circuit  inductance  was  fixed  and  the 
condenser  variable),  indicate  that,  if  the  resistance  of  the  detector  is  not 
too  great,  very  much  greater  selectivity  with  equal  loudness  of  signals  is 
obtained  by  tuning  the  detector  circuit,  with  the  detector  directly  in  the 
circuit  as  in  fig.  83.  No  absolute  figures  are  at  hand  as  to  the  effect  of 


124 


MANUAL   OF    WIRELESS    TELEGRAPHY. 


TO  AER? AL 


FIG.  84  VALVE   RECEIVER -MARCDN1- 


TO  AERIAL 

WIRELESS    SPECIALT 
APPARATUS    CO. 


FIG.   85    RTSSliNDEN     INTERFERENCE   PREVENTER 


FIG.   86 


FIG.  87.— Magnetic  Detector— Marconi. 


MANUAL    OF    WIKELESS    TELEGRAPHY. 


125 


shunting  the  detector  around  a  closed  tuned  circuit  as  in  figs.  80  and  8@, 
but  results  obtained  in  distance  of  communication  show  this  method  equal 
if  not  superior  to  any  other,  and  it  would  seem  that,  if  the  detector  has  a 
resistance  such  as  would  prevent  sharp  resonance  from  being  obtained 
when  placed  directly  in  the  closed  circuit,  shunting  it  will  assist  in 
producing  sharp  resonance  and  together  with  tuning  the  closed  circuit 
make  a  more  efficient  arrangement. 


FIG.  88. 

179.  Eeceiving  sets,  such  as  shown  in  fig.  80,  were  first  introduced  by 
Stone  and  used  later  by  Marconi.  The  intermediate  tuned  circuit  in 
these  sets  is  called  the  weeding  out  circuit.  Provision  is  made  for  switch- 
ing the  detector  to  the  weeding  out  circuit  when  very  sharp  tuning  is 
unnecessary,  since  there  is  loss  of  range,  due  to  loss  of  energy  in  so  many 
transfers. 

The  Fessenden  interference  preventer,  shown  in  fig.  86,  attains  select- 
ivity in  a  different  manner  from  that  just  described.  The  currents 
induced  in  the  aerial,  from  whatever  cause,  have  two  possible  paths  to 
earth;  one  of  these  paths  is  tuned  to  the  wave  length  it  is  desired  to 
receive,  while  it  is  supposed  that  waves  of  other  lengths,  or  static  dis- 
charges, out  of  tune  with  either  leg,  will  divide  themselves  equally  be- 
tween the  two  legs  and  produce  no  effect  on  the  untuned  detector  circuit. 

Attention  is  invited  to  figs.  81  and  82,  showing  the  DeForest  and  Shoe- 
maker looped  receiving  circuits.  These  differ  from  the  other  circuits 
illustrated  in  that  the  induced  currents  are  in  the  same  direction  on  the 
two  sides  of  the  loop  and  like  a  double-ended  sending  aerial  induce  a 
maximum  potential  at  some  point  in  the  .loop  whose  electrical  distance 
from  the  point  of  origin  of  the  disturbance  is  the  same  for  each  side. 
The  wave  length  of  a  looped  circuit  ungrounded  is  therefore  the  same  as 
that  of  one-half  of  it  ungrounded  and  the  wave  length  grounded  is  twice 
the  electrical  length  of  the  loop.  In  other  words,  one-half  the  loop  can 
be  considered  as  a  shunt  of  the  same  period  as  the  other  half.  From  this 
point  of  view  the  DeForest  detector  circuit  is  practically  the  same  as 


126  MANUAL    OF    WIRELESS    TELEGRAPHY. 

fig.  83  and  the  Shoemaker  circuit  can  be  considered  as  one  having  a 
detector  directly  in  the  open  circuit  and  shunted  by  a  variable  con- 
denser. 

Figs.  84  and  88  represent  the  valve  and  audion  receiver  circuits.  In 
fig.  84  the  valve  is  shunted  around  a  tuned  closed  circuit;  in  fig.  88  it  is 
in  a  closed  untuned  circuit.  Fig.  87  shows  the  magnetic  detector  in  a 
tuned  open  circuit,  provision  being  made  to  shunt  a  variable  condenser 
around  it. 

The  above  figures  illustrate  practically  all  methods  of  tuning  receiving 
circuits  and  of  connecting  detectors  to  them.  Detailed  instructions  for 
the  use  of  each  set  are  furnished  with  it. 

180.  We  wish  the  sending  aerial  to  be  a  good  radiator,  but  not  so 
good  that  it  will  give  a  whip  crack  discharge.  We  want  its  oscillations 
to  be  persistent  enough  to  require  for  their  best  reception  a  receiving 
aerial  tuned  to  the  period  of  the  sender,  and  as  a  present  standard  we 
have  set  for  the  sender  a  damping  considerably  less  than  .2,  so  that  it 
makes  fifteen  complete  oscillations  before  the  oscillating  current  falls  to 
.1  of  its  original  value.  We  want  the  receiving  aerial  to  radiate  as  little 
as  possible;  but  to  so  combine  the  energy  of  the  fifteen  waves  that  the 
highest  maximum  is  produced  in  the  aerial,  if  the  detector  is  in  the  open 
circuit,  in  the  closed  receiver  circuit,  if  the  detector  is  there  or  in  shunt 
around  it. 

If  the  sending  aerial  is  coupled  so  as  to  send  out  waves  of  two  lengths, 
there  appears  to  be  no  question  that  the  coupling  of  the  receiving  circuits 
should  be  such  that  if  they  acted  as  senders  they  would  send  out  waves 
of  these  lengths,  or  so  loosely  coupled  that  their  natural  period  is  that  of 
the  arriving  wave  containing  the  most  energy.  If,  in  the  case  of  very 
loosely  coupled  circuits  or  those  supplied  with  quenched  spark  "gaps,  but 
one  wave  length  is  being  generated,  receiving  circuits  should  also  be 
loosely  coupled  or  should  be  coupled  so  that  the  transfer  of  energy  from 
the  open  to  the  closed  circuit  and  the  damping  of  the  latter  (with  the 
detector,  however  connected)  is  at  such  a  rate  that  a  maximum  current 
in  the  closed  circuit  is  reached  at  the  instant  the  open  circuit  has  come 
to  rest  after  being  set  into  vibration  by  the  passing  wave  train  and  has 
radiated  or  transferred  all  its  induced  energy.  This  is  analogous  to  the 
statement  relative  to  the  quenching  of  the  closed  sending  circuit  (throw- 
ing it  out  of  tune)  when  the  open  circuit  has  reached  its  first  maximum. 
In  the  case  of  reception  after  the  closed  circuit  has  reached  its  first 
maximum  the  rectified  current  in  the  case  of  crystal  detectors  or  the 
battery  current  in  the  case  of  electrolytic  detectors  has  also  reached  its 
maximum. 

However,  further  investigation  is  necessary  before  definite  statements 
as  to  the  best  coupling  of  receiver  circuits  can  be  made,  and  until  such 
time  the  apparent  best  obtained  by  trial  in  each  set  must  be  used. 


MANUAL    OF    WIRELESS    TELEGRAPHY.  127 

TYPES  OF  RECEIVING  INDUCTANCES  AND  CONDENSERS. 

181.  A  variable  receiving  condenser  usually  consists  of  semi-circular 
metal  plates  separated  by  air  dielectric,  alternate  plates  being  fixed.    The 
others  are  movable  on  an  axis,  by  turning  which,  any  desired  amount  of 
the  movable  plates  can  be  included  between  the  fixed  plates.     The  axis 
carries   a  pointer  which   moves  over  a  scale  graduated  in   degrees   or 
directly  in  microfarads.     If  used  in  connection  with  a  fixed  inductance, 
the  scale,  Mke  a  wave  meter,  which  in  this  case  it  becomes,  may  be  grad- 
uated directly  in  wave  lengths.     Some  of  the  Stone  receiving  sets  had 
sliding  glass  plate  condensers,  and  the  Pierce  sets,  step-by-step  variable 
condensers  in  the  receiving  circuits,  but  the  revolving  plate  type  described 
above  is  practically  a  standard  and  is  illustrated  in  fig.  96.      (Pierce 
wave  meter.) 

Variable  condensers  now  supplied  have  the  limits  of  their  capacity 
marked  on  the  name  plate  in  microfarads. 

182.  Variable  inductances  include  the  step-by-step  and  roller  types. 
The  former  is  sometimes  made  up  of  plug  steps,  giving  a  limited  number 
of  changes,  one  section  of  a  coil  being  varied  at  a  time,  or  it  may  be  a 
cylindrical  coil  of  insulated  wire  wound  on  hard  rubber,  glass  or  por- 
celain, one  point  in  each  turn  being  bare  and  connections  being  made  by 
a  slider  giving  as  many  adjustments  as  there  are  turns  of  wire  in  the 
coil. 

In  the  DeForest  pancake  tuners  the  coil  was  a  flat  spiral  of  insulated 
wire  on  glass,  one  point  in  each  turn  being  bared  so  as  to  form  an  arc  of 
a  circle,  the  end  of  an  arm  pivoted  at  the  center  of  this  circle  making 
contact  at  any  desired  point.  Shoemaker  sets  (fig.  82)  have  a  single 
roller  inductance,  the  bare  wire  being  wound  in  a  spiral  groove  on  an 
ebonite  cylinder.  A  sliding  contact  on  a  rod  parallel  to  the  cylinder 
works  in  the  groove  and  is  pressed  against  the  wire  by  a  spring.  By 
revolving  the  cylinder  an  infinite  number  of  adjustments  can  be  obtained. 

Fessenden  sets  (figs.  79  and  82),  have  double  roller  inductances,  by 
turning  which,  the  wire  can  be  reeled  from  one  roller  to  another  as 
desired.  On  one  roller  the  turns  are  insulated  from  each  other  and  on 
the  other  they  are  short  circuited  so  that  any  desired  length  can  be  re- 
tained in  circuit.  None  of  the  above  types  of  variable  inductances  can  be 
readily  mounted  so  as  to  vary  the  mutual  induction  between  them  by  any 
definite  amount.  They  are  not  entirely  suitable  for  loose  coupling.  For 
this  reason  the  preferred  types  of  receiving  circuits  are  made  up  of  fixed 
inductances  (or  those  varied  by  plug  steps)  mounted  so  that  they  can 
either  be  pulled  apart  or  one  coil  revolved  so  as  to  change  its  plane  and 
hence  the  mutual  induction  with  reference  to  the  other  or  others.  Ke- 
ceiving  inductances  (variometers)  mounted  like  variable  condensers  are 
now  being  manufactured.  Their  self-induction  can  be  varied  quickly 


MANUAL    OF    WIRELESS    TELEGRAPHY. 

and  conveniently  and  close  adjustment  of  period  (tuning)  made  with 
them  or  with  the  variable  condensers. 

From  the  formula  for  damping  d=  9        it  can  readily  be  seen  that  a 

very  pronounced  natural  period — a  stiff  circuit — can  not  be  obtained 
unless  the  self-induction  is  large  compared  with  the  total  resistance  (in- 
cluding the  radiation  resistance). 

Variometers  have  a  constant  D.  C.  resistance,  since  the  entire  length 
of  wire  is  always  in  circuit.  In  order  that  this  resistance  should  not  be 
too  high  compared  with  the  self -induction,  it  is  specified  that  the  D.  C. 
resistance  shall  not  exceed  4  ohms  per  millihenry. 

Practically  all  inductances  are  wound  on  hard  rubber  or  glass — a 
material  like  air,  which  is  a  good  insulator,  with  no  hysteresis  loss  is  the 
ideal  material  for  the  purpose.  In  winding,  dead  ends,  which  are  a  source 
of  loss,  should  be  avoided. 

One  variable  inductance  of  fig.  83  is  hinged  so  that  the  coupling  can 
be  varied  by  a  combined  movement  away  and  of  rotation  with  reference 
to  the  inner  coil.  (See  fig.  111.) 

Fig.  86  illustrates  the  l-P-7'6  receiving  set,  of  which  a  great  many  are 
in  use. 

In  these  sets  the  coupling  between  the  open  and  closed  circuits  is 
varied  by  sliding  the  closed  circuit  inductance  on  a  graduated  bar  parallel 
to  its  axis  instead  of  revolving  it  as  in  the  Telefunken  receiving  set. 
(See  fig.  Ilia.) 

The  closed  circuit  of  these  sets  has  been  calibrated  and  curves  drawn 
showing  the  wave  lengths  for  all  settings  from  150  up  to  4450  meters. 
These  curves  are  furnished  with  the  sets  and  (with  very  loose  couplings 
so  that  the  two  circuits  have  but  one  period)  the  wave  length  of  received 
signals  can  be  read  directly.  Similar  curves  have  been  made  and  supplied 
with  some  of  the  Telefunken  receiving  sets.  Additional  loading  coils  for 
very  long  waves  are  now  being  supplied. 

Figs.  84  and  88  illustrate  the  valve  and  audion  receiving  sets.  The 
detectors  in  these  sets  are  alike  except  that  the  resistance  of  the  audion 
is  decreased  as  compared  with  the  valve  by  an  E.  M.  F.  from  a  local 
battery  connected  as  shown  in  fig.  88  (the  negative  terminal  to  the 
lamp).  It  will  be  noted  that  an  inductively  connected  low  resistance 
telephone  is  used  with  the  Marconi  (Fleming)  valve  in  fig.  84, 

DETECTORS. 

183.  There  are  but  two  types  of  detectors  now  in  general  use :  Crystal 
or  rectifying  detectors,  and  the  electrolytic.  Coherers  and  microphones 
are  practically  obsolete,  and  comparatively  few  of  the  magnetic  and 
audion,  or  valve  detectors,  have  been  installed.  All  types  of  detectors  in 


MANUAL   OF   WIRELESS   TELEGRAPHY.  129 

use  are  self -restoring.  Generally  speaking  all  require  to  be  put  on  open 
circuit  while  sending  to  preserve  them  from  injury  due  to  induced 
potentials  and  currents. 

THE  ELECTROLYTIC  DETECTOR. 

184.  It  consists  of  a  fine  platinum  wire  just  touching  an  electrolyte 
made  either  of  a  20$  solution  of  nitric  or  sulphuric  acid  or  an  alkali. 
Of  these  the  nitric  acid  solution  is  preferred.  The  other  electrode  is  also 
of  platinum.  The  containing  cup  (fig.  79)  is  made  quite  small  so  that 
the  cohesive  power  of  the  electrolyte  will  prevent  splashing  in  a  sea  way. 
The  electrolytic  detector  must  have  the  fine  wire  terminal  connected  to 
the  positive  pole  of  the  local  battery  (fig.  79),  otherwise  the  device  is 
not  operative. 

Dr.  Austin  states  that  the  higher  the  frequency  the  finer  the  wire 
should  be  and  that  the  depth  of  immersion  does  not  matter  if  the 
detector  is  not  directly  in  series  in  the  closed  circuit. 

When  a  current  flows  through  the  electrolyte  the  latter  is  decomposed 
(the  action  being  called  electrolysis)  liberating  oxygen  at  the  anode  and 
hydrogen  at  the  cathode.  The  accumulation  of  these  non-conducting 
gases  on  the  electrodes  interferes  with  the  passage  of  the  current,  which 
soon  ceases  to  flow  and  the  cell  is  then  said  to  be  polarized. 

The  fine  wire  anode  is  then  insulated  by  the  oxygen,  which  forms  the 
dielectric  of  a  small  condenser,  of  which  one  conducting  surface  is  the 
electrolyte  and  the  other  the  wire  point. 

The  critical  potential  of  the  detector  is  just  below  that  necessary  to 
break  down  this  insulating  layer  of  oxygen  and  is  determined  by  increas- 
ing the  potential  at  the  detector  terminals  by  means  of  the  potenti- 
ometer until  a  bubbling  or  hissing  sound  is  heard  in  the  receiving 
telephone ;  then  resistance  is  cut  in  until  this  sound  just  ceases. 

When  electric  oscillations  are  impressed  on  this  condenser  the  polariza- 
tion layer  breaks  down  and  permits  a  pulse  of  direct  current  from  the 
battery  to  pass  through  the  cell  and  telephone.  As  soon  as  the  oscilla- 
tions cease  the  polarization  is  restored. 

Except  when  they  are  very  strong  the  loudness  of  the  sounds  produced 
in  the  telephone  is  an  exact  measure  of  the  energy  of  the  oscillations 
passing  through  the  cell. 

This  constancy  of  action  of  the  electrolytic  cell  is  utilized  as  a  means 
of  comparing  the  sensitiveness  of  detectors,  the  standard  being  the  sen- 
sitiveness of  an  unjacketed  platinum  wire  electrode  .0002  in  diameter  in 
a  solution  of  20$  nitric  acid. 

Glass  jacketed  electrodes  formed  by  sealing  the  wire  in  glass  (the  two 
having  the  same  coefficient  of  heat  expansion)  have  been  used,  but  are 
less  reliable  and  in  general  less  sensitive  and  are  no  longer"  supplied. 


130  MANUAL    OF    WIRELESS    TELEGRAPHY. 

Some  of  these  glass  points  were  made  hook  shaped,  the  hook  pointing 
upward  to  facilitate  depolarizing  but  no  increase  in  sensitiveness  was 
noted  on  this  account. 

With  the  Shoemaker  receiving  sets  was  furnished  what  was  called  a 
primary  cell  detector.  The  electrolyte  used  was  a  20$  solution  of  sul- 
phuric acid  and  the  other  electrode  was  a  zinc  rod  amalgamated  with 
mercury,  which  in  the  acid  solution  gave  a  difference  of  about  .7  volt 
between  zinc  and  platinum.  No  local  battery  was  required  (fig.  82).  At 
times  this  detector  compared  favorably  with  the  one  just  described,  but 
was  in  general  more  irregular  and  less  sensitive  in  its  action. 

In  all  electrolytic  detectors  very  strong  signals  or  static  discharges 
produce  actual  sparking  or  an  explosive  action  in  the  electrolyte,  which 
destroys  the  platinum  point  and  an  operator  must  be  constantly  on  the 
lookout  to  protect  his  point  from  burning  out.  The  best  results  in 
electrolytic  detectors  have  been  obtained  with  a  distance  between  electrodes 
of  approximately  J  inch. 

RECTIFYING  DETECTORS. 

185.  There  are  certain  substances  which  when  brought  together  in  not 
too  close  contact  have  the  property  of  producing  a  direct  current  when  an 
alternating  current  or  electrical  oscillations  are  sent  through  them.  The 
cause  of  this  action  is  not  yet  known.  Among  these  substances  are  car- 
bon in  contact  with  steel,  tellurium  with  aluminum  or  galena,  silicon 
with  any  of  the  ordinary  metals,  and  certain  crystals. 

The  first  of  the  crystal  detectors  to  be  supplied  was  General  Dun- 
woody's  carborundum  crystal  detector. 

Since  rectifying  detectors  permit  the  passage  of  current  in  but  one 
direction,  they  produce  pulses  of  direct  current.  These  pulses,  if  strong 
enough,  can  be  heard  in  a  telephone  so  that  local  batteries  are  not  re- 
quired, although  a  slight  increase  of  sensitiveness  is  noted  in  some  de- 
tectors with  an  E.  M.  F.  across  the  terminals  of  the  detector  of  about  0.2 
volt. 

Rectifying  detectors  are  connected  in  receiving  circuits  in  the  same 
manner  as  the  electrolytic. 

Their  sensitiveness  for  general  use  is  practically  equal  to  the  electro- 
lytic and  their  simplicity  makes  them  the  most  suitable.  They  are  in 
general  less  sensitive  to  injury  from  static  discharges,  strong  signals,  or 
induced  currents  from  sending,  than  the  electrolytic,  but,  like  coherers, 
different  crystals  of  the  same  material  vary  widely  in  sensitiveness  and 
sensitive  spots  in  any  crystal  have  to  be  found  by  trial  and  when  found 
are  not  constant.  They  are  thus  not  as  capable  of  quick  readjustment 
as  the  electrolytic,  but  their  other  advantages  are  such  as  to  be  con- 
clusive as  regards  their  use. 


MANUAL    OF    WIRELESS    TELEGRAPHY.  131 

The  carborundum  detector  when  first  introduced  was  simply  held 
between  two  points  or  wrapped  with  copper  wire  for  one  connection,  with 
a  needle,  knife  edge,  or  more  blunt  piece  of  metal  for  the  other.  It  was 
later  found  that  embedding  a  large  part  of  the  crystal  in  a  conductor 
such  as  solder  or  a  mercury  paste,  and  thus  limiting  the  rectification  to 
one  contact  only,  produced  much  better  results  and  carborundum  crystals 
have  been  found  equal  in  sensitiveness  to  some  of  those  now  generally 
utilized. 

Pickard's  silicon  detector  followed  the  carborundum  and  is  still  in 
use  but  it  has  been  largely  superseded  by  the  Perikon  &  Pyron,  supplied 
with  the  receiving  set  illustrated  in  fig.  86.  The  Perikon  detector  con- 
sists of  two  crystals,  chalcopyrites  and  zincite.  A  number  of  zincite 
crystals  are  held  in  a  conducting  disc,  a  crystal*  of  chalcopyrites  is 
mounted  so  that  it  can  .be  brought  into  contact  with  any  part  of  any  of 
the  zincite  crystals  at  will,  and  the  pressure  between  the  two  regulated. 
In  the  adjustment  for  maximum  intensity  of  signals,  the  exact  degree  of 
pressure  and  the  most  favorable  points  of  contact  are  of  importance. 
These  can  only  be  ascertained  by  trial  and  test  with  the  testing  buzzer. 

The  sensitiveness  of  the  Perikon  may  be  approximately  doubled  by 
connecting  a  battery  across  its  terminals  so  as  to  give  approximately  0.2 
volt.  The  positive  pole  must  be  connected  to  the  single  crystal. 

The  Pyron  consists  of  a  crystal  of  iron  pyrites  in  contact  with  a 
metal  point  like  the  silicon.  This  is  very  satisfactory  for  strong  signals 
and  constant  in  its  action.  The  iron  pyrites  is  more  sensitive  when  the 
pressure  of  the  metal  point  is  adjustable.  The  area  of  contact  is  also  a 
determining  factor  of  sensitiveness;  comparatively  fine  points  will  dis- 
cover sensitive  places  on  irregular  crystals,  which  blunt  points  will  not. 

The  Perikon  is  more  sensitive  and  must  be  protected  against  strong 
signals.  The  zincite  is  the  crystal  injured  by  strong  signals.  It  should 
not  be  subjected  to  heavy  pressures  or  grinding  from  the  chalcopyrite. 
When  deadened  the  zincite  crystals  can  be  made  operative  by  scrubbing 
them  with  a  bristle  brush  wet  with  carbon  bisulphide,  then  with  soap  and 
water  and  then  rinsing  with  fresh  water  and  drying.  In  damp  weather 
or  in  tropical  climates  this  detector  is  improved  by  spreading  a  drop  of 
paraffin  oil  over  the  surface  of  the  crystals.  This  comment  applies  to  the 
silicon  also. 

VACUUM  TUBE  DETECTORS. 

186.  The  two  forms  in  use  are  Marconi  valve  detectors  and  the  DeFor- 
est  audion.  This  detector  invented  by  Fleming  is  a  rectifier  permitting 
the  passage  of  current  in  one  direction  only.  It  consists  of  a  special 
incandescent  lamp  (see  fig.  84),  operated  by  a  12-volt  storage  battery  and 


132  MANUAL    OF    WIRELESS    TELEGRAPHY. 

having  a  small  sheet  or  cylinder  of  metal  held  in  the  bulb  near  the  fila- 
ment. Lamp  filaments  when  glowing  emit  negative  electricity,  which 
carries  away  part  of  the  filament  and  causes  the  darkening  of  the  bulb 
seen  on  old  carbon  lamps.  The  vacuum  thus  becomes  a  conductor  in  one 
direction  only.  It  is  not  found  to  be  a  very  sensitive  one. 

Eeferring  to  fig.  88,  in  the  audion,  a  local  battery  with  variable  volt- 
age as-  connected  across  the  lead  to  the  filament  and  the  lead  to  the 
metal  electrode,  the  positive  pole  of  the  battery  being  connected  to  the 
metal  plate.  A  rheostat  for  regulating  the  voltage  of  the  storage  battery 
is  also  supplied.  The  battery  voltage  increases  the  fall  of  potential  across 
the  space  between  the  filament  and  the  plate,  and  this,  in  connection  with 
the  regulation  of  the  voltage  of  the  filament,  renders  the  detector  more 
sensitive  than  with  the  connections  shown  in  fig.  84. 

MAGNETIC   DETECTORS. 

187.  The  operation  of  magnetic  detectors  depends  on  the  fact  that 
when  iron  is  being  magnetized  its  magnetization  is  somewhat  delayed  in 
time  behind  the  impressed  magnetizing  force,  and  when  in  this  condition 
the  iron  is  very  sensitive  to  any  change  in  the  magnetizing  force,  a 
very  small  increase  of  which  will  produce  a  momentarily  large  increase 
in  the  strength  of  the  magnetic  field. 

Many  patents  have  been  issued  for  various  forms  of  magnetic  detectors, 
the  best  known  and  the  most  largely  used  of  which  is  Marconi's  patented 
in  England  in  1902. 

In  its  present  form  it  consists  of  a  flexible  band  of  silk-covered  iron 
wires,  moved  by  clockwork  around  two  pulleys  which  support  it.  A  glass 
tube,  through  which  the  band  passes,  has  a  primary  "winding  of  insulated 
wire  in  series  with  the  aerial  and  a  secondary  winding  forming  a  closed 
circuit  through  a  telephone.  Close  to  the  secondary  windings  are  placed 
similar  poles  of  two  horse-shoe  magnets,  which  magnetize  the  iron  band 
slowly  moving  under  them.  Electric  oscillations  in  the  primary  winding, 
produced  by  passing  electric  waves,  produce  momentary  changes  in  the 
magnetization  of  the  iron  band  under  the  magnets,  and  these  changes 
induce  oscillating  currents  in  the  secondary  winding  which  produce 
sounds  in  the  telephone. 

An  elementary  diagram  of  this  magnetic  detector  is  shown  in  fig.  87. 
It  requires  no  local  battery,  and,  not  being  subject  to  burn-outs  except 
from  very  large  currents,  it  is  a  very  convenient  instrument,  but  is  not 
as  sensitive  as  those  previously  described,  especially  for  short  wave 
lengths.  There  are  other  methods  of  connecting  this  detector  than  that 
shown  in  fig.  87,  but  since  comparatively  few  magnetic  detectors  are  in 
use  they  are  not  shown  here. 


MANUAL    OF    WIRELESS    TELEGRAPHY. 


133 


COHERERS  AND  LODGE-MUIRHEAD  DETECTOR. 

188.  Coherers  being  practically  obsolete  are  not  described.  They  are 
illustrated  in  fig.  89. 

Of  the  many  other  kinds  of  detectors  that  have  been  used,  the  Lodge- 
Muirhead,  which  would  work  either  with  a  telephone  or  recorder,  was  the 
most  sensitive  and  reliable. 


SLABY   ARCO   COHERER 


FIG.  89 


LODGE-MUIRHEAD 
COHERER 


FIG.   90 


It  is  illustrated  in  fig.  90  and  consists  of  a  polished  steel  disc  rotated 
by  clockwork,  its  edge  just  touching  the  edge  of  a  globule  of  mercury 
covered  by  a  film  of  oil.  A  pad  which  rubs  against  the  disc  keeps  it  clean 
and  bright.  This  coherer  may  be  direct  or  inductively  connected  in  or 
to  the  aerial.  Its  conductivity  changes  sufficiently  to  relay  a  current  for 
working  a  siphon  recorder  so  that  it  is  suitable  for  use  in  connection  with 
determining  longitudes  by  wireless  telegraphy. 

It  is  also  self-restoring  and  can  therefore  be  used  with  a  telephone. 


134  MANUAL    OF    WIRELESS    TELEGRAPHY. 

TESTING   BCZZERS. 

189.  A  testing  buzzer  with  its  battery  of  one  cell,  its  condenser  and 
circuit,  is  a  miniature  sending  set  and  an  important  auxiliary  of  every 
receiving  set.     The  oscillations  set  up  in  its  circuit  induce  currents  in 
the  receiving  circuits,  which  serve  by  their  effect  to  determine  the  sensi- 
tiveness and  readiness  for  operation  of  the  detector.     A  testing  buzzer 
outfit  furnished  with  the  Telefunken  sets  is  shown  in  fig.  91,  the  con- 
nections of  that  supplied  with  the  l-P-76  receiving  sets  in  fig.  92.    The 
condenser  is  the  Western  Electric  Co.'s  21-J. 

RECEIVING  TELEPHONES   AND  ACCESSORIES. 

190.  The  low  resistance  telephones  in  ordinary  use  are  not  suitable 
for  wireless  work  on  account  of  the  high  resistance  of  the  detectors,  which 
may  be  several  thousand  ohms.     Specially  made  telephones  are  required 
to  produce  the   best  effect.     The  magnet  wire  has  very  thin   silk  or 
enamel  insulation.     A  length  of  wire  whose  resistance  is  approximately 
equal  to  that  of  the  detector- can  be  efficiently  used.   This  is  from  1000 
to  2500  ohms  in  each  of  the  double  head  telephones  supplied. 

.  For  low  frequencies,  telephones  with  adjustable  diaphragms  are  found 
to  be  about  ten  times  as  sensitive  as  the  ordinary  type  with  a  fixed  dis- 
tance between  diaphragms  and  magnets. 

This  advantage  decreases  as  the  frequency  approaches  the  present 
standard  of  500  cycles  (1000  sets  of  sparks  per  second),  but  is  still 
sufficient  to  warrant  the  retention  of  the  adjustable  diaphragm  type. 

At  stations  where  it  is  necessary  to  listen  on  two  wave  lengths  at  the 
same  time,  one  half  of  the  head  set  is  connected  to  one  receiving  set  and 
the  other  half  to  the  other  receiving  set. 

In  some  Marconi  sets  low  resistance  receiving  telephones  are  used, 
connected  through  a  step-down  transformer.  (See  fig.  84.) 

Batteries  and  potentiometers  are  used  with  receiving  telephones,  their 
connections  being  as  shown  in  figs.  77  to  89. 

In  order  to  produce  sound,  intermittent  work  must  be  done  on  a  tele- 
phone diaphragm  at  a  certain  minimum  rate.  (See  arts.  100  and  131.) 
In  other  words  we  must  apply  a  certain  power  to  it — power  being  rate  of 
doing  work.  The  frequency  must  be  within  the  limits  of  audibility. 
(Art.  218.) 

It  appears  that  with  rectifying  detectors  we  obtain  this  power  directly 
from  the  aerial,  while  with  the  electrolytic,  the  power  from  the  aerial 
only  works  the  detector  as  a  relay — the  power  used  in  making  sound  in 
the  telephone  coming  from  the  local  battery. 

Difficulties  surrounding  accurate  measurement  of  the  very  minute 
quantities  involved  make  the  above  statement  subject  to  modification. 
We  do  not  yet  know  exactly  how  a  detector  acts. 


MANUAL    OF    AVIRELESS    TELEGRAPHY. 


135 


FIG.  91. — Wireless  Telegraph  Test  Buzzer.    For  Ships. 


-vr 

1 

PLAT/  NO  M  COWTAC 

II 

"\ 

BU22ER 

J 

FIG.  92. 


136  MANUAL   OF   WIRELESS    TELEGRAPHY. 

TELEPHONE  RELAYS. 

191,  Those  now  in  service  are  called  ampliphones.  If  they  prove  to  be 
constant  and  reliable  they  will  be  supplied  for  general  use,  (a)  to  enable 
ordinary  messages  to  be  read  without  the  use  of  a  head  telephone,  (b)  as 
a  call,  (c)  to  increase  the  absolute  difference  between  signals  of  different 
strengths  thus  enabling  the  message  desired  to  be  read  through  inter- 
ference or  static,  (d)  to  step-up  signals  so  weak  that  they  could  not  other- 
wise be  read  and  thus  increase  the  range  of  communication,  (e)  as  a 
resonance  device  responding  within  limits  to  a  single  spark  frequency, 
thus  cutting  out  interference,  (f)  for  separating  signals  of  different 
wave  train  frequencies  so  that  several  messages  of  different  frequencies 
can  be  received  at  the  same  time  on  the  same  aerial,  (g)  to  automatically 
record  incoming  signals. 

Coherer  detectors  change  their  resistance  sufficiently  to  work  a  relay 
which  actuated  a  call,  tapper  and  recording  apparatus.  The  induced 
currents  rectified  by  crystal  and  valve  detectors  are  too  weak  to  produce 
visible  material  movement  unless  a  "  string  "  galvanometer  is  used  with 
them  when  signal  can  be,  read  and  recorded  at  commercial  speeds  and 
the  same  is  true  of  the  direct  currents  produced  by  the  momentary 
depolarization  of  electrolytic  detectors. 

It  has  been  found,  however,  that  these  currents  will  produce  sufficient 
movement  of  the  diaphragm  of  a  receiving  telephone  to  alter  its  pressure 
on  a  microphonic  contact,  this  alteration  being  enough  to  change  the 
conductivity,  and  thus  increase  or  decrease  the  current  in  a  circuit  con- 
taining the  contact,  a  battery  and  another  telephone.  This  change  in 
current  moves  the  diaphragm  of  the  second  telephone  and  its  movements 
can  either  be  read  directly  as  sound  or  made  to  change  the  current  in 
another  circuit  by  change  of  pressure  on  another  microphonic  contact. 
One  or  more  of  these  microphonic  relays  produces  sufficient  action  in  a 
loud  speaking  telephone  to  be  heard  in  the  operating  room. 

When  used  as  a  resonance  relay  the  relay  diaphragms  are  mounted 
so  as  to  have  a  pronounced  mechanical  period  of  vibration  and  act  as 
wave  filters  or  weeding  out  circuits,  responding  most  efficiently  only  to 
wave  trains  of  a  frequency  the  same  as  their  own.  The  sound  produced 
by  the  last  one  in  circuit  (the  loud  speaking  telephone)  may  be  intensified 
by  attaching  to  it  an  air  pipe  whose  note  is  the  same  as  that  of  the 
diaphragm  in  vibration. 

RECORDING  APPARATUS. 

192.  The  use  of  recording  apparatus  was  necessarily  abandoned  when 
coherers  were  no  longer  used.  It  is  possible  that  microphonic  relays  re- 
ferred to  in  the  preceding  article  will  again  permit  the  use  of  recording 
and  calling  apparatus.  Both  tend  directly  to  economy  in  the  operation 
of  wireless  stations,  by  reducing  the  number  of  operators  to  a  minimum. 


Chapter  VII. 

INSTALLATION,  ADJUSTMENTS,  CASE,  OPERATION. 

INSTALLATION. 

193.  For  installation  ample  room  is  available  at  all  shore  stations. 

On  board  ship,  a  room  having  about  100  square  feet  of  floor  space, 
with  no  dimension  less  than  6  feet,  should  be  provided  for  the  installa- 
tion and  operation  of  a  wireless  telegraph  set.  The  operating  room 
should  be  well  ventilated  and  lighted,  as  nearly  sound-proof  as  practi- 
cable, and  free  from  vibration.  The  exact  location  of  the  room  is  not  of 
great  importance,  provided  a  good  lead  to  it  for  the  aerial  can  be  ob- 
tained. The  farther  this  lead  is  from  large  conducting  bodies  the  better. 

The  room  should  have  a  well-insulated  entrance  for  the  aerial  and 
should  be  fitted  with  an  operating  table  about  2-J  feet  wide,  not  less  than 
7  feet  long,  and  of  convenient  height  for  working  the  sending  key  while 
sitting  down. 

The  table  should  be  strongly  built  of  dry,  well-seasoned  wood. 

The  instruments  should  be  mounted  on  the  table  so  that  they  are  at 
safe  sparking  distance  from  each  other  and  from  any  part  of  the  oper- 
ating room. 

The  receiving  instruments  should  be  as  far  away  from  the  sending 
instruments  as  practicable.  The  induction  coil  or  transformer  may  be 
mounted  on  the  bulkhead  or  under  the  table.  In  any  case  it  should  be 
where  its  terminals  are  not  likely  to  be  touched  accidentally.  The  motor 
generator  is  preferably  installed  near  the  operating  room,  but  outside  of 
it.  It  may  be  installed  in  the  operating  room  or  in  the  dynamo  room. 

The  connections  between  all  parts  of  the  sending  and  receiving  instru- 
ments should  be  as  direct  as  possible,  and  in  the  case  of  sending  instru- 
ments they  should  be  of  large  surface  and  well  insulated  by  air  or 
other  nonconductors.  Sharp  turns  in  connecting  wires  should  be  avoided 
on  account  of  brush  discharges,  which  always  start  at  corners.  The  effect 
is  the  same  as  if  the  electricity  were  traveling  too  fast  to  turn  corners. 

The  necessity  for  bringing  a  number  of  leads  to  the  combination  switch 
for  sending  or  receiving  detracts  considerably  from  the  simplicity  of  the 
installation  and  to  a  slight  extent  from  the  efficiency  of  the  set  as  a  whole. 

High-potential  leads  should  be  kept  well  away  from  low-potential 
leads,  and  where  they  cross  it  should  be  nearly  at  right  angles. 

The  ground  connections  should  be  electrically  good  and  of  large  area. 

The  receiver  (and  the  transmitter  when  practicable)  should  be  wired  up 


138 


MANUAL    OF    WIRELESS    TELEGRAPHY. 


before  installation,  requiring  only  securing  in  place  and  attachment  to 
aerial  and  ground  for  receivers;  to  power,  aerial  and  ground  for  trans- 
mitters. 

The  sending  appliances  should  be  so  arranged  that  the  leads  connecting 
the  condenser,  inductance,  and  spark  gap  of  the  transmitter  will  be  of 
minimum  length. 

At  shore  stations  means  should  be  provided  outside  the  operating  room 
for  disconnecting  the  aerial  from  the  operating  circuit  and  connecting  it 
direct  to  ground. 

On  board  ship  a  lightning  switch  should  be  installed  which  when  in 
use  will  safely  and  completely  disconnect  the  aerial  from  all  of  the  re- 
ceiver and  transmitter  circuits  and  connect  it  direct  to  ground. 

The  aerial  should  be  well  insulated  where  it  enters  the  operating  room 
and  where  it  passes  through  decks  or  bulkheads.  Porcelain  or  glass 
insulators  are  best  for  this  purpose. 

When  necessary  .to  guy  the  aerial  at  any  point  an  insulator  should  be 
used  in  the  guy  line.  The  suspending  or  hoisting  halliards  of  the  aerial 
should  be  insulated.  Two  types  of  suitable  strain  insulators  for  this 
purpose  are  shown  in  figs.  93  and  94. 


FIG.  93    AERIAL  INSULATOR  -   BUCK  LINK-  STRAIN "10 


FIG.  94   AERIAL  WITH  LOCKE  N2  IO5  INSULATORS 


MANUAL    OF    WIRELESS    TELEGRAPHY. 


139 


194.  The  large  momentary  currents  in  aerials  produce  large  inductive 
effects  in  conductors  near  and  parallel  to  them.    This  is  more  noticeably 
the  case  in  wire  stays  of  masts,  shrouds,  braces,  etc. 

It  should  also  be  noted  that  an  aerial  wire  parallel  and  near  to  a  long 
lighting  or  power  lead  may  induce  sufficiently  high  potentials  in  the  lead 
to  puncture  the  insulation  and  cause  sparking  between  it  and  the  con- 
ductors in  the  vicinity  of  combustible  material,  thereby  causing  fires. 
Or  it  may  puncture  the  insulation  and  cause  a  burn-out  of  'an  armature, 
field,  or  transformer.  All  of  these  effects  have  been  experienced.  They 
are  especially  frequent  and  dangerous  in  the  wireless  sending  apparatus. 

PROTECTIVE   DEVICES. 

195.  Eigging  of  masts  at  shore  stations  is  divided  into  short  lengths  by 
strain  (usually  locust)  insulators.    Wire  braces  are  served  near  the  mid- 
dle with  chokes  made  of  No.  26  B.  &  S.  soft  iron  wire  for  a  length  of 
about  10  feet. 

Wire  leads  at  shore  stations  are  lead  covered  and  the  lead  grounded. 
Leads  in  conduit  on  board  ship  are  protected  by  the  conduit  being 
grounded. 

Wires  in  the  open  should  be  protected  by  chokes  of  soft  iron  wire,  as 
for  braces,  or  have  an  armored  cover  well  grounded. 

To  conduct  to  ground  induced  high  potential  at 

(a)  Terminals  of  primary  of  transformers. 

(b)  Terminals  of  armature  of  alternator. 

(c)  Terminals  of  shunt  field  of  alternator. 

(d)  Terminals  of  shunt  field  of  motor. 

(e)  Terminals  of  armature  of  blower  motor. 

The  protective  devices  shown  in  fig.  95  are  installed. 


FUSE: 


-I 


t 


t 


FIG.  95. — Protective  Appliance. 

The  protective  devices  consist  of  two  1-microfarad  condensers  con- 
nected in  series,  the  middle  connection  grounded  and  the  two  outer 
terminals  connected  by  strip  copper  leads  (as  short  as  possible)  to  the 
apparatus  to  be  protected.  In  parallel  with  each  condenser  is  a  per- 

10 


140  MANUAL   OF   WIRELESS    TELEGRAPHY. 

• 

manently  set  spark  gap  about  the  width  of  thin  tissue  paper.  Each  leg 
of  the  device  is  fused  with  a  3-ampere  cartridge  fuse.  Graphite  resist- 
ance rods  were  formerly  used  for  this  purpose.  Only  the  construction 
described  above  is  now  supplied. 

In  addition  to  the  above,  safety  spark  gaps  are  fitted  to  receiving  tele- 
phones. Secondary  terminals  of  transformers  are  protected  by  chokes 
made  from  the  leads,  and  by  safety  spark  gaps  permanently  set  at  the 
maximum  safe  sparking  distance. 

196.  All  wireless  telegraph  sets  are  fitted  with  a  multiple  switch  which 
in  the  sending  position  disconnects  the  receiving  circuits  from  the  aerial 
and  ground  and  breaks  detector  and  telephone  connections  as  may  be 
necessary  to  protect  them  from  induced  high  potentials. 

When  in  the  receiving  position  this  switch  opens  the  primary  or  sec- 
ondary circuit  of  the  transformer  and,  if  the  motor  generator  is  in  the 
operating  room,  operates  a  relay  for  opening  the  field  of  the  motor,  or  in 
some  cases  short  circuits  the  armature  to  bring  it  to  a  stop  quickly.  This 
switch  should  also  stop  the  blower  motor. 

The  necessity  for  the  above  detracts  considerably  from  the  simplicity 
of  an  installation. 

ADJUSTMENTS. 

197.  This  includes  calibration  and  tuning.     Since  the  periods  of  the 
open  circuits  of  both  sending  and  receiving  sets  depend  on  the  aerial  with 
which  they  are  used  and  the  constants  of  the  latter  can  not  usually  be 
predetermined,  the  open  circuit  has  to  be  calibrated  after  the  set  is  in- 
stalled.    The  closed  circuit  of  receiving  sets  can  readily  be  calibrated 
before  installation.    Also  the  closed  circuit  of  sending  sets,  if  wired  up 
before  installation. 

All  adjustable  inductances  now  supplied  have  a  scale  indicating  in 
millihenries  the  value  of  the  amount  in  circuit  at  each  point  of  variation. 
All  fixed  condensers  have  the  value  of  their  capacity  in  microfarads 
engraved  on  the  name  plate  of  the  condensers,  and  all  variable  condensers 
have  the  range  of  their  capacities  marked  on  the  name  plate. 

The  wave  length  of  a  circuit  made  up  of  a  calibrated  inductance  and 
a  calibrated  capacity  as  above  can  be  calculated  from  the  formula  :  Wave 
length  in  meters  =  1884.9  5  VlJL.  When  C  is  in  microfarads,  L  is  in 
micro-henries,  the  formula  being  derived  from  the  fundamental:  T= 


For  calibrating  the  aerial  circuit  and  other  circuits  not  already  cali- 
brated wave  meters  are  supplied,  which  are  used  as  receivers  to  calibrate 
sending  circuits  and  as  senders  to  calibrate  receiving  circuits.  After 
calibration  the  adjustment  of  these  circuits  to  the  same  wave  length  and 
to  the  desired  coupling  is  called  tuning. 


MANUAL    OF    WIEELESS    TELEGRAPHY.  141 

198.  To  be  completely  in  time,  a  sending  set  should  have  the  circuit 
made  up  of  the  A.  C.  armature  winding,  primary  leads,  and  primary 
winding  of  transformer,  in  resonance   (tune)  with  that  formed  by  the 
sending  condenser  and  secondary  winding  of  the  transformer.   Both  cir- 
cuits should  be  in  resonance  with  the  alternator  frequency. 

The  closed  sending  circuit  should  be  in  resonance  with  the  open  cir- 
cuit and  the  coupling  and  decrement  of  the  open  circuit  such  as  to  afford 
the  necessary  selectivity  to  the  receiving  circuits  with  the  best  efficiency 
of  radiation. 

Receiving  circuits  to  receive  from  such  a  sender  should  be  in  resonance 
with  each  other  and  with  the  sending  circuits  and  should  have  the  same 
coupling  as  the  sending  circuits.  The  telephone  diaphragm  should  be 
in  resonance  with  the  wave  train  (alternator)  frequency  and  with  the 
operator's  ear. 

As  was  previously  stated,  instead  of  designing  telephone  diaphragms 
for  resonance  with  alternators,  we  design  the  alternator  for  resonance 
with  the  telephone  diaphragm. 

Resonance  is  thus  seen  to  be  a  vital  quality  in  wireless  telegraph  cir- 
cuits. (1)  Resonance  of  alternator  frequency  with  primary  sending 
circuit.  (2)  Resonance  of  primary  circuit  with  secondary  sending  cir- 
cuit. (3)  Resonance  of  closed  oscillating  circuit  with  open  radiating 
circuit.  (4)  Resonance  of  coupled  receiving  circuits  with  each  other  and 
with  coupled  sending  circuits.  (5)  Resonance  of  telephone  diaphragm 
with  primary  frequency.  (6)  Resonance  of  human  ear  with  telephone 
diaphragm. 

Of  these  (1),  (2)  and  (5)  are  elements  of  design  and  are  not  change- 
able at  the  will  of  the  operator.  (1)  and  (2)  can  be  varied  to  a  certain 
extent  by  reactance  regulators  which  in  the  latest  Telefunken  sets  are 
provided  for  both  circuits;  but  it  is  preferable  to  cover  this  feature  in 
the  original  design  of  the  transformers.  (3)  and  (4)  are  entirely  under 
the  operators  control  and  on  them  the  efficiency  of  the  set  depends. 

WAVE  METERS  AND  THEIR  USE. 

199.  Standard  calibrated  oscillating  circuits  called  wave  meters,  which 
are  adjustable  at  will  to  a  great  number  of  known  wave  lengths  are  used 
for  calibrating  and  tuning. 

When  adjusted  to  resonance  with  the  circuit  to  be  measured  the  fact 
is  indicated  according  to  the  type  of  wave  meter  by  a  maximum  of  sound 
in  a  telephone,  a  maximum  glow  in  a  vacuum  tube,  a  maximum  reading 
of  a  hot  wire  ammeter  or  the  brightness  of  a  glow  lamp. 

The  Pierce  wave  meter  uses  a  telephone  exclusively.  It  is  suitable  for 
determining  resonance  only.  The  Donitz  meter  uses  a  hot  wire  ammeter 
or  air  thermometer,  whose  maximum  reading  indicates  resonance  and 


142  MANUAL    OF    WIRELESS    TELEGRAPHY. 

lower  readings  the  relative  amount  of  energy  received  when  the  wave 
length  of  the  wave  meter  is  varied.  These  readings  can  be  plotted  as  a 
curve.  Wave  meters  now  furnished  can  be  used  either  with  a  detector  and 
telephone  or  with  a  hot  wire  ammeter  or  galvanometer  for  determining 
resonance.  Wave  meters  are  also  fitted  with  small  spark  gaps  and  spark 
coils  so  that  they  can  be  used  as  senders  for  calibrating  receiving  circuits. 
Instructions  for  the  use  of  wave  meters  are  supplied  with  the  instru- 
ments. 

200.  In  determining  wave  lengths  three  methods  for  fixing  the  con- 
denser reading  for  maximum  current  may  be  used.  1.  For  a  rough 
determination  the  apparent  position  of  maximum  reading  may  be  fixed 
by  a  single  observation.  2.  For  a  more  accurate  determination  the  maxi- 
mum reading  of  the  hot-wire  ammeter  or  galvanometer  may  be  noted, 
and  the  condenser  pointer  be  moved  first  to  the  right  until  the  current 
reading  falls  by  a  certain  amount,  and  then  to  the  left  of  the  maximum 
position  until  it  falls  to  an  equal  amount.  The  position  half  way  be- 
tween these  two  condenser  readings  may  be  taken  as  the  true  maximum. 
3.  The  values  of  the  current  reading  corresponding  to  a  large  number  of 
condenser  readings  on  each  side  of  the  maximum  may  be  taken,  and  a 
curve  plotted  having  condenser  readings  as  abscissas  and  current  readings 
as  ordinates.  From  this  curve  the  most  accurate  possible  position  of  the 
maximum  can  be  obtained. 

Where  wave  meters  are  to  be  used  only  for  the  determination  of  the 
position  of  maximum  resonance,  small  vacuum  tubes  are  sometimes 
placed  in  parallel  with  the  inductance,  and  these  light  up  when  the  poten- 
tial across  the  inductance  reaches  a  maximum. 

For  measuring  the  wave  length  of  any  sending  set  as  it  is  being  used 
it  is  only  necessary  to  bring  the  wave  meter  into  position  near  a  single 
loop  in  either  the  antenna  or  ground  connection,  taking  care  that  there 
is  no  direct  induction  from  the  helix  into  the  wave  meter  coil,  close  the 
key  for  a  long  dash  and  ascertain,  by  moving  the  pointer  over  the  grad- 
uated scale,  the  position  of  resonance  as  indicated  above,  i.  e.,  by  tele- 
phone H.  W.  A.  (hot-wire  ammeter)  or  galvanometer.  This  will  gen- 
erally be  on  the  longer  wave  or  ff  upper  hump  "  since  in  stations  sending 
out  two  waves  the  longer  wave  contains  the  most  energy  and  is  the  most 
easily  read.  To  locate  the  short  wave  ((f  lower  hump")  it  may  be  neces- 
sary to  couple  the  wave  meter  helix  quite  closely  with  the  loop.  In  sets 
having  loose  coupling  and  those  supplied  with  quenched  spark  gaps,  but 
one  position  of  resonance  should  be  found. 

To  ascertain  the  wave  length  of  the  closed  circuit  disconnect  the  aerial, 
couple  the  wave  meter  with  the  helix  and  proceed  as  before.  But  one 
wave  length  will  be  found.  This,  if  the  same  as  the  first  one  measured, 
will  show  that  there  is  but  one  length  of  wave  being  generated  and 
radiated.  The  two  operations  above  described  can  be  performed  in  less 


MANUAL    OF    WIRELESS    TELEGRAPHY.  143 

than  five  minutes.  To  ascertain  the  wave  length  of  the  aerial  is  not  so 
easy.  To  do  so  disconnect  the  closed  circuit,  place  a  temporary  spark 
gap  in  the  ground  lead  of  the  aerial,  connect  leads  from  the  transformer 
to  each  side  of  the  gap  and,  in  ordinary  ship  sets  where  the  capacity  of 
the  aerial  is  small,,  also  put  a.  Leyden  jar  across  the  gap.  Place  the  wave 
meter  near  the  aerial  inductance  and  adjust  to  resonance.  This  reading 
should  be  the  same  as  that  found  for  the  closed  circuit. 

201.  If  both  open  and  closed  circuits  read  425  and  the  upper  hump  is 
found  to  be  450  and  lower  hump  390,  the  percentage  of  coupling  is 

45^-390 


If  but  one  hump  is  found  and  that  at  425,  with  an  ordinary  spark  gap, 
the  circuits  are  very  loosely  coupled.  This  fact  can  also  be  determined 
approximately  by  an  inspection  of  the  sending  helix.  If  direct  con- 
nected and  but  one  wave  length  is  found,  it  will  also  be  found  that  the 
number  of  turns  common  to  the  two  circuits  is  very  small  or  less  than 
one  turn.  If  inductively  connected,  that  the  active  parts  of  the  two 
helices  are  not  close  together,  in  other  words,  the  mutual  induction  is 
very  small.  The  single  wave  found  on  loose  coupled  sets  using  an  ordi- 
nary gap  is  not  as  sharp  as  that  found  on  the  closed  circuit  read 
separately.  Some  mutual  induction  is  necessary  to  transfer  energy  so 
that  the  two  waves  can  not  quite  merge  into  one. 

The  above  measurements  will  show  whether  the  open  and  closed  circuits 
are  in  resonance  and  what  wave  length  or  lengths  are  being  sent  out  as 
adjusted. 

202.  Tuning  curves  showing  the  wave  length  for  any  adjustment  of 
each  circuit  should  be  made,  plotting  the  wave  meter  readings  as  wave 
lengths  horizontally  on  the  bottom  of  a  sheet  of  cross  section  paper 
(standard  A  sheet)  and  the  number  of  turns  of  the  helix  for  each  read- 
ing on  the  side  vertically. 

Draw  smooth  curves  (see  figs.  98  and  101)  through  the  points  thus 
found  for  both  the  open  and  closed  circuits.  An  inspection  of  these 
curves  will  show  how  many  turns  must  be  included  in  each  circuit  for 
any  given  wave  length.  When  set  by  these  tuning  curves  to  the  same 
wave  length  the  accuracy  of  the  curves  can  be  checked  by  the  reading  of 
the  H.  W.  A.  If  the  setting  is  correct,  any  change  in  either  circuit  will 
decrease  the  reading  of  the  H.  W.  A.  It  must  be  remembered  as  stated 
elsewhere  that  it  generally  takes  a  change  of  several  turns  of  inductance 
to  change  the  wave  length  of  the  open  circuit  appreciably,  while  a  change 
of  less  than  one  turn  will  change  the  wave  length  of  the  closed  circuit 
considerably,  so  that  it  is  much  easier  to  throw  the  two  circuits  out  of 
resonance  by  changing  the  closed  circuit  turns  than  by  changing  the 
open  circuit  turns. 


144 


MANUAL    OF    WIRELESS    TELEGRAPHY. 


It  must  also  be  remembered  that  the  tuning  curve  for  a  closed  circuit 
is  only  correct  for  the  capacity  in  the  circuit  at  the  time  the  measure- 
ments were  made. 

The  removal  of  a  jar  from  the  condenser;  change  of  shape  or.  length 
of  leads  to  helix;  bad  connections  to  jars — each  and  all  change  the  wave 
length  of  the  closed  circuit  and  throw  it  out  of  resonance  with  the  open 
circuit  with  marked  decrease  in  radiation. 

The  H.  W.  A.  can  be  used  to  adjust  two  circuits  to  the  same  wave 
length  but  it  gives  no  indication  of  what  that  wave  length  is. 

When  a  wave  meter  is  available  it  is  shown  above  that  to  take  a  reading 
of  the  closed  circuit  wave  length  requires  but  a  minute's  work. 

The  wave  length  of  the  open  circuit  with  the  same  number  of  turns 
included  varies  little  from  any  cause,  and  if  the  insulation  and  ground 
are  good  the  causes  of  decreased  radiation  should  be  looked  for  in  the 
spark  gap  or  in  bad  connections,  broken  jars,  etc.,  in  other  parts  of  the 
closed  circuit. 

It  has  been  proposed  where  the  coupling  is  such  that  two  wave  lengths 
are  radiated  to  throw  the  two  circuits  slightly  out  of  resonance  to  in- 
« crease  the  proportion  of  the  total  energy  in  the  long  wave;  but  no  dis- 
tinct gain  in  efficiency  has  been  noted. 

It  is  better  to  loosen  the  coupling  to  the  point  where  but  one  wave  can 
be  found,  even  if  this  is  beyond,  as  it  usually  will  be,  the  point  where 
the  highest  hot  wire  ammeter  reading  is  obtained. 

It  must  be  remembered,  however,  that  efficiency  varies  directly  as  the 
H.  W.  A.  reading  and  the  latter  must  be  maintained  as  high  as  possible 
consistent  with  sending  out  waves  of  but  one  length. 


A  -  BINDING  POSTS. 
C  -  VARIABLE  CAfiacirr. 

D-  DYNAMOMETER. 

L-  INDUTANCE. 

P  -  POINTER. 

T  -  SWITCH. 

L  -  LONG  WAVE  LENGTHS 

s  -  ShORT  WAVE  LENGTHS. 


FIG.  96. 


203.  Fig.  96  shows  the  Pierce  wave  meter  referred  to  in  art.  181. 
This  meter  is  used  for  calibrating  and  determination  of  resonance  by 
means  of  sound  only. 


MANUAL  OF  WIRELESS  TELEGRAPHY.  145 

INSTRUCTIONS  FOR  USING  THE  PIERCE  WAVE  METER  OF  THE  MASSACHU- 
SETTS WIRELESS  EQUIPMENT  Co. 

A. CALIBRATION  OF  SENDING  STATION. 

1.  To  make  the  Instrument  ready  for  use. — Take  off  the  cover,  fold 
back  the  hinged  loop,  and  attach  the  leads  of  the  telephone  receiver 
(stowed  in  cover  of  box)  to  the  two  binding  posts  near  together  to  the 
left  of  the  metric  scale. 

2.  Placing  the  Instruments. — Place  the  instrument  near  the  circuit 
whose  wave  length  is  to  be  determined,  and  by  turning  the  loop  on  its 
projecting  horizontal  axis  bring  it  in  such  a  position  (parallel)  that  it 
will  be  linked  by  the  magnetic  lines  from  the  oscillating  circuit.     The 
proper  distance  from  the  loop  to  the  oscillating  circuit  depends  on  the 
intensity  of  the  oscillations.     When  the  observations  are  to  be  made 
directly  on  the  Ley  den  jar  circuit  the  wave-meter  loop  may  be  one  or  two 
meters  from  the  discharge  circuit,  while  if  observations  are  to  be  made 
on  parts  of  the  circuit  in  which  the  currents  are  feebler,  this  distance  may 
be  reduced  to  a  few  centimeters. 

In  setting  up  a  station  the  wave  lengths  of  the  various  parts  of  the  cir- 
cuit may  be  determined  separately  in  the  usual  manner. 

When  the  station  is  already  set  up  ready  for  use,  the  wave  length  or 
the  two  wave  lengths  it  is  radiating  may  be  determined  by  placing  the 
wave  meter  near  the  wire  to  ground  or  the  wire  to  antenna  with  the  loop 
of  the  instrument  in  the  plane  of  the  wire. 

3.  Regulation  of  Spark. — Make  the  spark  of  the  station  short  and 
adjust  the  current  in  the  discharge  circuit  so  that  the  spark  is  clear  and 
sharp. 

4.  Taking  Observations. — Put  the  telephone  receiver  to  the  ear  and 
with  the  hand  holding  the  receiver,  touch  one  of  the  metallic  tips  of  the 
lead  where  it  enters  the  receiver.    This  will  shut  out  the  general  hum  due 
to  the  alternating  current  in  the  transformer.    If  no  such  hum  is  present 
it  is  not  necessary  to  touch  the  terminal  in  this  manner. 

Now  with  the  free  hand  turn  the  handle  in  the  center  of  the  instru- 
ment and  set  for  a  maximum  in  the  telephone. 

In  making  these  observations  the  switch  to  the  right  must  be  either 
on  "  L"  or  "  S."  This  switch  should  be  on  "  L"  for  long  waves  and  on 
"  S  "  for  short  waves.  With  the  switch  on  "  S  "  read  the  position  of  the 
pointer  or  red  scale.  The  position  of  the  pointer  for  a  maximum  sound 
in  the  telephone  is  the  wave  length  in  meters.  If  the  switch  is  on  "  L  " 
the  black  scale  should  be  read  and  gives  the  wave  length  in  meters. 

In  case  the  sounds  in  the  telephonic  receiver  are  too  loud  for  accurate 
settings,  their  intensity  may  be  reduced  either  by  moving  the  instrument 
farther  away,  or  more  conveniently,  by  turning  the  receptor  loop  so  that 


146  MANUAL   OF   WIRELESS   TELEGRAPHY. 

the  inductive  action  is  diminished.    In  the  final  setting  it  is  desirable  to 
have  the  sound  in  the  telephone  just  audible  at  resonance. 

5.  Use  of  Geissler  Tube  for  Demonstrations. — If  it  is  desired  to  use  a 
Geissler  tube  with  the  instrument,  leave  the  telephone  connected  in,  con- 
nect one  terminal  of  the  tube  to  the  nearer  left-hand  post  along  with  the 
telephone  lead  and  the  other  terminal  of  the  tube  to  the  idle  binding 
post  at  the  back  of  the  instrument.  The  tube  is  then  in  parallel  with 
the  condenser  of  the  wave  meter  and  should  glow  at  the  proper  setting. 

B. — CALIBRATION    OF   RECEIVING    STATION. 

204.  6.  Use  of  Wave  Meter  as  Sending  Station. — Take  off  the  tele- 
phonic receiver  of  the  wave  meter  and  put  in  its  place  the  spark-gap 
supplied  with  the  apparatus.    This  attachment  has  a  coil  in  its  base  of 
approximately  the  proper  inductance  to  replace  the  telephone.     Use  the 
wave  meter  as  a  sending  station  and  for  any  given  wave  length  of  the 
wave  meter  set  the  receiving  station  to  resonance  as  in  receiving  messages 
from  a  distant  source. 

7.  Spark-Coil. — In  using  the  wave  meter  as  a  sending  station  it  should 
be  actuated  by  a  small  spark-coil.    Attach  the  leads  from  the  secondary 
of  the  spark-coil  to  the  two  sides  of  the  wave  meter  spark-gap.    This  gap 
should  be  opened  not  more  than  a  few  hundredths  of  an  inch  (.1  or  .2 
millimeters).     When  the  gap  is  too  wide,  sparks  occur  inside  the  wave 
meter  between  the  plates  of  the  condenser. 

8.  Position. — The  wave  meter  when  used  as  a  sending  station  should 
be  placed  about  three  meters  from  the  receiving  antenna,  and  should  not 
be  approached  too  closely  by  the  observer  who  is  listening  at  the  telephone 
of  the  receiving  station,  since  conduction  or  induction  through  the  body 
of  the  observer  and  along  his  telephone  leads  will  result  in  a  general  hum 
that  can  not  be  tuned  out. 

C. — PRECAUTION  AND  CARE  OF  THE  INSTRUMENT. 

9.  Do  not  attempt  to  open  the  telephone  receiver,  and  do  not  change  or 
break  the  leads  of  the  telephone  as  injury  to  the  telephone  will  disturb  the 
calibration. 

10.  In  stowing  away  the  apparatus  be  careful  to  leave  the  pointer  free 
from  obstructions.    To  this  end,  whenever  the  instrument  is  to  be  trans- 
ported it  is  advisable  to  disconnect  the  telephone  and  place  it  in  the  clamp 
in  the  cover  of  the  box  with  the  leads  secured  under  the  wooden  buttons. 

11.  The  receptor  loop  should  be  folded  in  with  knob  upward  so  that 
pointer  can  be  rotated  under  the  loop  without  interference. 

205.  Fig.  97  is  a  diagram  of  the  original  Donitz  wave  meter  with  air 
thermometer.    A  hot-wire  ammeter  is  now  used  with  this  instrument  or 
a  detector  connected  with  a  galvanometer.    This  wave  meter,  called  by  its 
inventor  an  ondameter,  is  used  for  other  measurements  as  well  as  for 


MANUAL   OF   WIRELESS   TELEGRAPHY. 


147 


FIG.  97.— Slaby  Arco  Donitz  Wave  Meter. 


148  MANUAL   OF    WIRELESS   TELEGRAPHY. 

calibrating.  The  instructions  given  in  the  preceding  article  for  the  use 
of  the  Pierce  wave  meter  apply  in  general  to  all  wave  meters. 

In  calibrating  closed  sending  circuits,  the  shape,  as  well  as  the  length 
of  the  leads,  must  be  taken  into  consideration.  This  shape  must  .be  the 
permanent  one.  In  sets  now  being  supplied  connections  of  the  helix  are 
made  so  as  to  avoid  any  change  of  shape  with  change  of  wave  length. 

In  calibrating  the  open  circuit  of  receiving  sets  the  same  difficulty  will 
be  found  in  obtaining  sharp  resonance  as  when  calibrating  open  sending 
circuits.  The  instructions  given  in  art,  200  should  then  be  followed; 
substituting  turns  of  inductance  or  variometer  pointer  for  condenser 
pointer,  since  in  this  case  the  wave  meter  is  being  used  as  a  sender  and 
readings  are  by  sound  or  galvanometer. 

206.  Fig.  98  shows  calibration  curves  of  closed  (1)  and  open  (2)  cir- 
cuits made  with  a  Donitz  meter  at  the  Guantanamo  wireless  station  in 
1906. 

In  addition  to  calibrating  sending  and  receiving  circuits  it  is  desirable 
to  measure  the  sending  current  and  also  the  received  currents. 

Calibrating  sending  and  receiving  circuits  enables  us  to  select  and  send 
and  set  our  instruments  to  receive  definite  known  wave  lengths  and  is  the 
first  requisite  of  tuning.  In  order  that  our  receiving  circuits  may  be 
selective,  i.  e.,  respond  only  to  the  wave  lengths  for  which  they  are 
adjusted  they  must  have  comparatively  large  self-induction.  In  other 
words,  they  must  be  what  are  known  as  stiff  or  rigid  circuits.  In  order 
that  a  wave  train  may  be  long  enough  to  build  up  current  in  a  rigid  re- 
ceiving circuit  the  sending  circuit  must  be  a  persistent  oscillator,  i.  e.,  it 
must  be  slowly  damped.  (Fig.  62.) 

It  must  not  be  forgotten  that  the  currents  in  a  very  persistent  oscilla- 
tor like  a  closed  sending  circuit  are  mostly  dissipated  in  heat,  while  we 
wish  to  have  their  energy  radiated  in  electric  waves. 

We  must  therefore  strike  a  mean  between  the  efficient  very  highly 
damped  sending  circuit  which  radiates  nearly  all  the  energy  it  receives 
in  one  or  two  waves,  but  which  affects  all  receiving  circuits  alike  and  the 
inefficient  persistently  oscillating  sending  circuit  which  dissipates  most 
of  its  energy  in  heat  but  which  is  favorable  for  selective  receiving. 

Sharp  tuning  or  selectivity  depends,  therefore,  on  self-induction  in  the 
radiating  circuit  as  well  as  in  the  receiving  circuits. 

207.  Curve  (7),  fig.  98,  shows  thermometer  readings  for  wave  meter 
settings   at   the   Guantanamo   station — between   900    and   2000   meters. 
These  readings  show  the  upper  hump  at  1650  meters,  lower  hump  at  1130 
meters,  with  -J  turn  inductance  in  closed  circuit — 5  J  turns  in  open  circuit. 

The  air  thermometer  readings  in  the  wave  meter  measure  the  received 
current  in  the  same  way  that  the  hot  wire  ammeter  in  the  aerial  measures 
the  sending  current.  The  readings  of  both  meters  vary  according  to  the 
heat  generated  by  the  currents  and  this  heat  varies  as  the  square  of  the 
current. 


MANUAL    OF    WIRELESS    TELEGRAPHY. 


149 


I      I 


CVw>/  * 


I 


K   ° 

i  "s 


ULJ_ 


150 


MANUAL    OF    WIRELESS    TELEGRAPHY. 


300 3iO 32O       33O 

WAVE  'LENGTHS  IN  METERS 
FIG.  99. 


MANUAL    OF    WIRELESS    TELEGRAPHY.  151 

Dr.  Austin  says  that  if  a  rectifying  detector  and  galvanometer  are  used 
for  measuring  the  received  currents  the  direct  currents  produced  are  also* 
proportional  to  the  square  of  the  oscillating  currents ;  so  all  these  ways  of 
measuring  are  directly  comparable.  (See  curve  7.)  The  maximum  wave 
meter  reading  is  25  at  1650  meters;  at  1800  meters  and  1480  meters  it 
reads  10.  By  changing  the  setting  of  the  wave  meter  either  way  150 
meters  we  reduce  the  strength  of  the  received  currents  in  the  value  of 
V25  to  VlO  or  approximately  5  to  3. 

Turn  now  to  curve  III,  fig.  99.  We  see  that  a  change  of  75  meters 
in  the  wave  meter  setting  changes  the  reading  from  a  maximum  of 
14  to  a  reading  of  1.  Curve  III,  fig.  99,  is  a  much  sharper  curve  than 
(7)  of  fig.  98.  The  same  kind  of  wave  meter  being  used  for  measuring 
the  received  currents  in  both  cases  we  conclude  that  the  sending  circuit 
in  fig.  99  is  a  more  persistent  oscillator  than  that  in  fig.  98.  Compare 
also  the  shape  of  curve  I,  fig.  99,  from  the  more  rapidly  damped  open  cir- 
cuit oscillating  alone,  with  the  shape  of  II,  produced  by  the  closed  circuit 
alone,  and  III,  produced  by  the  coupled  circuits. 

The  maxima  of  these  curves  have  no  direct  relation  to  each  other  since 
they  are  produced  by  different  amounts  of  radiated  energy  and  probably 
by  different  relative  positions  of  the  wave  meter  and  the  circuits.  It  is 
their  shapes  alone  that  are  the  subject  of  comparison  and  discussion.  The 
shape  of  each  curve  will  remain  the  same  whatever  the  position  of  the 
wave  meter  (receiving  circuit) .  Let  the  portion  of  each  curve  above  the 
heavy  line  X  Y  in  figs.  98  and  99  represent  the  range  of  audibility  at  any 
distance — say  100  miles  from  the  sending  set.  Thus  in  curve  II,  fig.  99, 
a  change  in  the  receiving  circuit  of  only  8  meters  from  the  position  of 
maximum  loudness  would  render  the  incoming  signals  inaudible,  while  in 
curve  7,  fig.  98,  a  change  of  150  meters  would  be  required  to  cut  out  sig- 
nals. In  neither  case  would  the  lower  hump  audibly  affect  the  receiving 
apparatus.  Sharp  tuning  is  not  possible  with  a  highly  damped  trans- 
mitter as  the  shape  of  these  curves  show.  Neither  is  it  possible  without 
stiff  receiving  circuits.  The  latter  should,  however,  be  variable;  that  is, 
capable  of  being  broadly  or  sharply  tuned  as  desired  (i.  e.,  it  should  be 
possible  to  switch  the  detector  from  a  highly  damped  to  a  rigid  circuit  or 
the  circuits  should  be  mounted  so  as  to  permit  wide  variations  of  coup- 
ling) .  There  is  no  more  possibility  of  escape  from  a  whip  crack  trans- 
mitter than  from  static. 

208.  In  addition  to  being  able  to  estimate  damping  from  tuning  or 
resonance  curves  we  can  measure  it  directly  as  follows : 

MEASUREMENT  OF  DAMPING. 

T> 

In  was  stated  (art.  117)   that  the  damping  of  any  circuit  8=-^— =~ 
where  R  is  the  resistance,  n  the  frequency  and  L  the  self-induction  of 


152 


MANUAL    OF    WIRELESS    TELEGRAPHY. 


the  circuit.  If  one  circuit  be  used  to  excite  another  and  if  either  of  the 
two  circuits  contains  a  variable  capacity,  we  may  plot  a  curve  connecting 
the  readings  of  the  variable  condenser  as  abscissas  and  the  current  in  the 
second  circuit  as  ordinates.  (See  fig.  100.)  This  is  the  resonance  curve 


=  750  M. 


Sl  +  B  =  o  038. 


60 


50 


I   40 

I 
o 


30 


o  20 

z 


10 


48  49  50  51  52 

CONDENSER  SETTING  IN   DEGREES. 

FIG.  100. — Resonance  Curve  Taken  with  Wave  Meter. 


of  the  two  circuits.    The  theory  of  coupled  circuits  shows  that  the  sum  of 
the  dampings  of  the  two  circuits  81  +  82  =  7r     Cm~C    */_._*!_  ^? 

^m  T       I m I 


where 


Cm  represents  the  position  of  the  condenser  in  degrees  for  most  perfect 
resonance,  and  Im  the  maximum  current  in  the  second  circuit  correspond- 
ing to  the  position  of  the  condenser  Cm,  and  where  I  represents  the  cur- 
rent in  the  circuit  corresponding  to  any  other  position  C  of  the  variable 
condenser.  This  formula  becomes  much  simplified  for  practical  pur- 


MANUAL   OF   WIRELESS   TELEGRAPHY.  153 

poses.,  and  gives  in  general  accurate  enough  results,  if,  instead  of  plot- 
ting a  complete  curve,  we  change  the  variable  condenser  so  that  for  the 
reading  G,  I2  =  %  Pm-  The  quantity  under  the  radical  then  becomes 

unity,   and  ^  +  B2  =  TrCm~G  .     Two  values  of   C  should   be  observed 
^m 

one  on  each  side  of  (7m,  and  the  mean  of  the  two  values  of  the  damping 
taken.  If  the  current  is  measured  by  means  of  a  thermo-e lenient  or  a 
perikon  detector  in  connection  with  a  galvanometer,  the  readings  of  the 
galvanometer  are  proportional  to  I2;  that  is  C  is  so  chosen  that  the  gal- 
vanometer deflection  is  reduced  to  one-half  that  observed  with  Cm.  If 
the  current  is  read  with  a  hot-wire  instrument  reading  directly  in  am- 
peres, then  the  reading  of  the  meter  corresponding  to  C  should  be  ——r 

of  that  corresponding  to  Cm,  since  1.41  =  V2.  This  expression  gives  the 
true  value  of  the  dampings  of  the  circuits  only  when  the  coupling  between 
them  is  extremely  loose. 

If  the  coupling  is  not  very  loose  between  the  two  circuits,  the  apparent 
value  of  the  damping  will  be  too  large.  The  proper  degree  of  coupling 
can  be  ascertained  by  observing  the  point  beyond  which  loosening  the 
coupling  does  not  decrease  the  damping.  If  the  damping  of  the  wave 

73 

meter  circuit  be  known  or  can  be  calculated  from  the  formula  80  =  -  .    T  , 

2nL 

by  subtracting  this  from  the  sum  of  the  two  dampings  we  get  at  once 
the  damping  of  the  other  circuit. 

If  we  wish  to  express  damping  in  terms  of  wave  length  A  instead  of 
capacity  or  inductance,  it  may  be  shown  mathematically  that  the  sum 

of  the  damping  81  +  82  =  27r  -^ — ,  where  as  before  A  is  the  wave  length, 

A 

which  reduces  the  square  of  the  received  current  to  one-half  of  that 
found  for  resonance  at  \m. 


154  MANUAL   OF    WIRELESS   TELEGRAPHY. 

209.  From  the  results  of  damping  measurements  it  has  been  found  that 
very  sharp  tuning  is  impracticable  when  a  wave  train  contains  less  than 
15  oscillations.  This  corresponds  to  a  decrement  of  .2  (see  fig.  62). 
Having  measured  the  damping  of  the  open  circuit  as  coupled  and  found 
it  too  large  it  is  necessary  to  add  inductance  in  order  to  decrease  it,  or  to 
weaken  the  coupling  in  order  that  the  total  resistance  R  may  be  decreased. 
If  it  is  not  practicable  to  change  the  wave  length,  the  aerial  must  be 
shortened  to  decrease  its  capacity  while  retaining  the  same  wave  length 
by  adding  inductance.  Loosening  the  coupling  also  decreases  the  damp- 
ing. 

Fig.  101  shows  a  resonance  curve  taken  from  a  loose  coupled  sending 
set,  showing  but  one  maxima  at  330  meters  with  5  turns  of  inductance  in 
the  open  circuit  and  less  than  -J  turn  in  the  closed  circuit.  This  curve 
is  steep  enough  to  permit  fairly  selective  receiving. 


MANUAL    OF    WIRELESS    TELEGRAPHY. 


155 


11 


156 


MANUAL   OF   WIRELESS   TELEGRAPHY. 


MANUAL   OF   WIRELESS    TELEGRAPHY.  157 

Fig.  102  shows  much  steeper  curves  taken  from  a  direct  connected 
quenched  gap,  500  cycle  set. 

The  position  of  the  two  small  humps  in  curve  I,  fig.  102,  taken  at  the 


— 

primary  variometer  indicates  a  coupling  of  -  -  =  22$.    This  is 

J  1  o 

by  no  means  very  loose  coupling,  but  the  curve  shows  that  the  aerial 
radiates  most  of  its  energy  while  oscillating  in  its  natural  period  (in  this 
case  975  meters)  and  that  when  so  oscillating  it  is  persistent  enough  to 
permit  very  sharp  tuning. 

Curve  II  in  fig.  102  taken  at  the  aerial  inductance  shows  but  one  maxi- 
mum which  practically  coincides  in  wave  length  with  the  maximum  of 
curve  I.  (  Curve  II  is  drawn  to  a  different  scale,  so  that  the  coincidence 
in  maximum  readings  is  only  apparent.  They  are  in  reality  smaller  for 
the  open  than  the  closed  circuit.) 

210.  Receiving  circuits  can  be  stiffened  without  changing  the  wave 
length  by  putting  a  condenser  in  series  to  decrease  the  capacity  and  then 
adding  inductance  to  keep  the  same  wave  length.  But  the  damping  of 
sending  circuits  can  not  be  conveniently  changed  in  this  way  on  account 
of  the  high  potentials  which  would  be  induced  in  the  series  condenser. 
The  method  of  measuring  damping  just  described  is  applicable  to  receiv- 
ing as  well  as  to  sending  circuits.  Receiving  circuits  have  in  general 
greater  resistance  than  sending  circuits,  but  this  is  limited  by  specifica- 
tions to  4  ohms  per  millihenry  in  order  not  to  injuriously  increase  the 
damping.  . 

For  measuring  the  sending  current  a  hot-wire  ammeter  is  installed 
directly  in  the  aerial  just  above  the  ground  connection. 

Curve  6,  fig.  98,  shows  hot-wire  ammeter  readings  in  open  circuit  for 
various  couplings  and  wave  lengths  at  the  G-uantanamo  station.  The 

maximum  reading  is  for  a  coupling  of 


The  highest  hot-wire  ammeter  reading  shows  that  the  circuits  are  in 
resonance  and  is  usually  taken  also  to  indicate  the  best  coupling;  but 
except  for  circuits  with  quenched  gaps  the  highest  H.  W.  A.  reading  is 
usually  obtained  with  a  coupling  which  causes  the  radiating  circuit  to  be 
too  highly  damped.  It  is  therefore  best  to  loosen  the  coupling  until  the 
shape  of  the  resonance  curves,  or  actual  measurements,  show  sufficiently 
small  damping;  and  then,  by  careful  adjustment  to  resonance,  attention 
to  connections,  to  spark  gap,  and  to  regulator,  get  the  highest  hot-wire 
ammeter  reading  that  can  be  obtained  with  that  coupling  and  wave  length. 

211.  In  order  that  the  performance  of  different  sets  can  be  compared 
it  is  necessary  that  all  hot-wire  ammeters  be  calibrated  for  reading  directly 
and  correctly  in  amperes. 

A  hot-wire  ammeter  which  reads  correctly  on  direct  current  should 
be  calibrated  for  high  frequency  as  follows  : 


158  MANUAL    OF    WIRELESS    TELEGRAPHY. 

First  remove  the  shunt  and  send  with  reduced  power  so  that  the  de- 
flections will  approximately  cover  the  scale.  This  can  be  done  either  by 
cutting  down  the  actual  power  or  by  loosening  the  coupling  between  the 
closed  circuit  and  aerial.  Note  the  deflections.  Then  close  the  shunt  and 
leaving  everything  else  unchanged  send  again  and  note  the  deflection. 
The  relation  between  the  two  deflections  gives  the  ratio,  for  this  wave 
length,  of  the  shunted  to  the  unshunted  readings.  If  any  other  wave 
length  is  used,  the  shunt  must  be  recalibrated  since  its  effective  resistance 
depends  on  the  frequency. 

Eeports  of  current  in  aerial  should  always  read  correctly  in  amperes 
and  be  accompanied  by  report  of  exact  frequency  and  input  to  transformer 
in  amperes  and  volts.  It  is  found  that  the  distance  of  transmission  varies 
directly  as  the  oscillating  current  in  the  aerial,  so  that  it  is  important  to 
ascertain  correctly  what  this  current  is. 

THE    SHUNTED    TELEPHONE    METHOD    OF    MEASURING   THE    INTENSITY    OF 

SIGNALS. 

212.  It  is  often  desirable  to  make  quantitative  determination  of  the 
intensity  of  incoming  signals,  especially  when  tests  are  being  made  of 
either  sending  or  receiving  apparatus.  This  can  be  done  if  the  station 
is  provided  with  an  electrolytic  receiver,  preferably  of  the  free-wire  type, 
and  a  resistance  box.  The  connections  are  shown  in  fig.  103. 


I  I        wwvww          :&  <•  -=y=- 

I     ^Z     i   T 

J /nnnoooooorx ^ 


FIG.  103. — Detector  Circuit  with  Shunted  Telephone. 

Here  L  and  L±  are  wires  running  to  the  receiving  circuit,  K  a  stopping 
condenser,  D  the  electrolytic,  T  the  telephone,  R  a  resistance  box  in  shunt 
across  the  telephones,  P  the  potentiometer,  and  C  a  choke  coil  to  prevent 
the  oscillations  running  around  through  R  and  P  instead  of  passing 
through  D  when  the  shunt  R  is  closed.  Two  60-ohm  telephones  form  a 
suitable  choke. .  Whatever  choke  coil  is  used,  it  should  be  tested  by  being 
placed  across  LLX.  If  the  choke  is  perfect  no  oscillations  will  pass 
through  it,  and  its  presence  across  LLX  will  not  diminish  the  loudness  of 
the  signals  in  the  telephones. 

The  measurement  of  the  intensity  of  signal  is  made  as  follows :  After 
the  receiving  circuit  and  detector  are  adjusted  to  give  maximum  loudness 
in  the  telephone,  the  shunt  resistance  R  is  closed  and  the  resistance  regu- 


MANUAL    OF    WIRELESS    TELEGRAPHY.  159 

lated  until  the  signal  just  remains  audible.  The  value  of  the  current 
pulses  c  in  the  telephone,  which  are  proportional  to  the  energy  of  the 
incoming  waves  in  the  detector,  is  expressed  by  the  following  formula, 
where  r  is  the  value  of  the  shunt,  and  t  is  the  resistance  of  the  telephones, 
and  c1  the  least  current  audible  in  the  telephones : 

r  +  t   j 
f> /ii  • 

r    C) 

c1  is  the  audibility  current,  and  the  signal  is  often  expressed  as  being 
so  many  times  audibility.  With  care  a  series  of  measurements  of  inten- 
sity may  be  made  to  agree  among  themselves  to  within  5  to  10  per  cent. 
A  station  is  tuned,  when  both  sending  and  receiving  circuits  are  cor- 
rectly calibrated,  coupled,  and  adjusted  to  the  standard  damping  and 
wave  length. 

213.  Inductances   and   capacities  can  be  directly  measured  by  wave 
meters  as  follows: 

MEASUREMENT  OF   INDUCTANCE  AND  CAPACITY. 

Inductance. — A  circuit  is  formed  containing  the  unknown  inductance, 
a  known  capacity  (one  or  more  standard  jars),  and  a  small  spark  gap. 
This  circuit  is  used  to  excite  the  wave  meter,  and  the  variable  condenser 
is  varied  until  a  maximum  current  in  the  wave  meter  is  obtained.  The 
two  circuits  being  then  in  resonance,  the  product  of  the  inductance  and 
capacity  in  each  is  the  same;  that  is,  LG  —  L^C^,  or  if  L  is  the  unknown 

T  ini 

quantity,  L  =  —7T- . 
C 

Capacity. — If  the  spark  circuit  is  made  up  with  a  known  inductance 

7"  V"^ 

and  unknown  capacity,  by  the  same  process  we  determine  that  C=  — =— . 

Li 

CARE  AND   OPERATION. 

214.  At  all  stations,  ship  and  shore,  the  best  results  are  invariably 
obtained  and  the  most  satisfactory  service  given  by  alert  and  careful 
operators  who  take  pride  in  the  condition  of  their  instruments.    Wireless 
telegraph  instruments  like  all  others  depend  for  their  efficiency  on  their 
condition  and  amply  repay  good  care. 

An  excellent  operator  once  said  that  no  matter  how  good  he  thought 
his  contacts  and  connections  were  he  always  found  that  by  going  over  them 
he  could  make  them  better  and  increase  his  sending  and  receiving 
efficiency.  A  routine,  which,  if  followed,  will  ensure  the  proper  care  of  a 
wireless  set,  is  given  in  Appendix  E. 

All  sliding  contacts,  especially  in  receiver  tuning  coils,  should  be  clean 
and  bright  and  free  from  foreign  matter.  Sending  key  contacts  should 
be  kept  clean  and  smooth  and  with  faces  parallel  to  each  other. 

Detectors  must  be  kept  in  their  most  sensitive  condition  and  frequently 
tested  by  means  of  the  buzzer  furnished  for  the  purpose. 


160  MANUAL   OF   WIRELESS   TELEGRAPHY. 

When  any  part -of  the  condenser  is  injured  it  should  be  immediately 
replaced  or  repaired.  Any  change  in  closed  or  open  circuit  without  a 
corresponding  change  in  the  other  throws  the  two  circuits  out  of  reso- 
nance and  greatly  decreases  the  sending  radius. 

If  the  capacity  in  the  condenser  must  be  decreased  for  any  cause  then 
in  order  to  retain  the  same  wave  length  the  inductance  in  the  closed 
circuit  must  be  increased. 

215,  The  following  general  instructions  apply  to  all  stations:  The 
operator  shall  wear  the  double  head  receiver  continuously  while  on  watch, 
except  when  necessary  to  communicate  otherwise  than  by  wireless.  He 
shall  satisfy  himself  by  frequent  testing  with  the  buzzer  that  his  detector 
is  sensitive,  and  while  in  the  vicinity  of  other  vessels  or  near  shore  stations 
and  using  a  detector  that  may  be  injured  by  strong  sending,  he  shall 
always  be  alert  to  protect  it  by  weakening  the  coupling  or  by  opening  the 
receiving  switch. 

He  shall  familiarize  himself  with  all  sending  and  receiving  connec- 
tions and  adjustments  and  be  able  to  tell  when  they  are  correct  and  to 
renew  them  when  necessary ;  but  he  shall  not  make  any  changes  in  any  of 
them  without  the  knowledge  and  permission  of  the  chief  electrician  or 
operator  in  charge. 

He  shall  be  capable  of  adjusting  the  spark  gap,  motor  and  generator 
rheostats  and  reactance  regulator,  so  as  to  obtain  the  necessary  output 
for  the  communication  to  be  made. 

He  shall  use  the  shortest  gap  and  the  least  power  that  will  enable  his 
messages  to  be  clearly  read.  The  spark  must  be  kept  white  and  crackling 
and  have  considerable  volume.  He  shall  be  vigilant  in  noting  and 
keeping  in  good  condition  all  sending  condenser  connections  and  in 
keeping  all  articles  or  instruments  which  might  be  injured  or  cause  a 
ground  or  sparking  well  clear  of  the  sending  apparatus  at  all  times. 

He  shall  not,  except  in  cases  of  emergency,  call  or  send  any  message, 
when  official  messages  are  being  sent  or  received  by  other  vessels  or 
stations  in  his  vicinity. 

He  shall  be  careful  to  file  correct  copies,  on  the  official  forms,  of  all 
messages  sent  and  received  by  him,  initialing  each  and  filling  in  time 
and  place  and  other  information  as  called  for  on  forms. 

He  shall  avoid  a  short  and  jerky  style  of  sending.  Dots  and  dashes 
and  intervals  must  be  of  proper  relative  lengths  as  shown  by  the  code  in 
order  that  the  sending  may  be  clear  and  legible.  Operators  must  en- 
deavor to  attain  fair  speed,  both  in  sending  and  receiving. 

Where  heavy  static  is  encountered,  dots  and  dashes  may  be  longer,  but 
must  preserve  their  relative  length.  The  generator  shall  be  run  only 
during  the  time  necessary  to  send  messages. 

Where  a  number  of  tunes  are  ordered  to  be  used  the  operators  shall  be 


MANUAL   OF   WIRELESS    TELEGRAPHY.  161 

careful  to  see  that  all  circuits  are  correctly  adjusted  before  attempting  to 
send. 

An  operator  shall  turn  the  station  over  to  his  relief  clean  and  neat. 

A  sending  set  with  all  connections  good,  closed  and  open  circuits  in 
resonance,  no  sparking  from  edge  of  condenser  jars  or  plates,  no  glow 
from  aerial  and  no  sparking  to  rigging,  is  utilizing  its  power  more 
efficiently  and  will  be  heard  farther  than  the  same  set  pushed  to  the  limit 
but  out  of  resonance  with  high  resistance  connections  and  sparking  at  all 
points. 

Messages  shall  not  be  sent  between  11.55  A.  M.  and  noon,  75th  merid- 
ian time,  in  the  Atlantic,  and  120th  meridian  time  in  the  Pacific. 
During  this  interval  naval  wireless  telegraph  stations  send  the  noon  time 
signal  for  the  use  of  navigators  in  comparing  chronometers. 

CODES. 

216.  For  official  use  between  ships  of  the  navy  and  between  them  and 
naval  shore  wireless  telegraph  stations  the  Continental  Morse  code  is  used. 

Commercial  shore  stations  in  the  United  States,  and  United  States 
coasting  vessels  use  American  Morse. 

All  foreign  stations,  ship  and  shore,  public  and  private,  use  Conti- 
nental Morse.  American  Morse  is  a  little  faster.  Both  codes  are  printed 
herein.  The  Continental  Morse  is  a  dash  and  dot  code  throughout  with 
a  maximum  of  four  elements  in  any  letter.  The  American  Morse  uses 
five  elements  in  the  letter  P,  four  elements  and  a  space  in  Y,  Z  and  &, 
and  a  long  dash  for  the  letter  L.  It  has  a  relatively  less  number  of 
dashes  than  the  Continental  code  and  is  on  that  account  faster. 

It  will  be  noted  that  A,  B,  D,  E,  G,  H,  I,  K,  M,  N,  S,  T,  U,  V  and  W 
(fifteen  out  of  the  twenty-six. letters  of  the  alphabet)  are  the  same  in  both 
codes. 

It  is  to  be  hoped  that  the  use  of  wireless  telegraphy  will  eventually 
bring  about  an  international  agreement  as  to  the  elements  for  the  re- 
maining eleven  letters  and  thus  provide  a  universal  code.  This  will 
facilitate  intercourse  between  United  States  ships  and  those  of  other 
nations  and  relieve  operators  of  the  necessity  of  learning  two  codes. 

When  it  is  desired  to  communicate  by  the  international  signal  book  (as 
between  two  vessels  whose  operators  do  not  use  the  same  language)  the 
"  call "  should  be  followed  by  the  letters  P  R  B  in  the  Continental  code. 

The  international  signal  of  distress  is ,  making  the 

letters  SOS  of  the  Continental  code. 

The  two  signals  given  above  were  adopted  at  the  International  Wire- 
less Telegraph  Conference  at  Berlin  in  1906.  The  United  States  has  not 
yet  ratified  the  convention  and  is  therefore  not  a  party  to  the  Inter- 
national Rules,  but  the  two  signals  above,  especially  the  signal  of  distress, 


162  MANUAL    OF    WIRELESS    TELEGRAPHY. 

are  generally  recognized.  The  most  important  rules  of  this  convention 
are  given  in  Appendix  C. 

The  rule  of  this  convention  that  all  stations  should  have  three  call 
letters  is  also  followed  in  the  United  States.  A  list  of  these  call  Letters 
is  published  by  the  Navy  Department  in  "  Wireless  Telegraph  Stations  of 
the  World  "  and  can  be  obtained  from  the  Government  Printing  Office. 

Information  relative  to  U.  S.  naval  shore  stations  and  shore  stations  in 
some  other  countries  is  issued  in  "  Notices  to  Mariners  "  and  shown  on 
pilot  charts  published  by  the  U.  S.  Naval  Hydrographic  Office.  The  rules 
governing  communicaticn  between  naval  shore  stations  and  private  ves- 
sels are  published  in  the  same  manner.  The  substance  of  these  will  be 
found  in  Appendix  B. 

The  Act  regulating  apparatus  and  operators  on  steamers,  which  goes 
into  effect  on  July  1,  1911,  will  be  found  in  Appendix  D. 

In  view  of  the  continually  increasing  use  of  wireless  telegraphy  it  is 
necessary  to  employ  concerted  methods  of  avoiding  interference  other  than 
static  caused  by  stations,  ship  and  shore,  in  the  same  vicinity  trying  to 
communicate  at  the  same  time,  using  the  same  wave  length. 

These  methods  are  not  yet  perfected,  but  are  in  outline  as  follows : 

(a)  Standard  calling  wave  lengths  for  ships  and  for  shore  stations. 
Say  600  meters  for  ships,  1000  meters  for  shore  stations. 

(b)  Standard  communicating  wave  lengths  or  tunes  different  from  the 
calling  tunes,  ranging  from  300  to  10,000  meters,  and  designated  by 
letters  of  the  alphabet  as  Tune  A-300  meters,  Tune  B-400  meters,  etc. 

(c)  Assigning  specific  tunes  (the  long  ones)  to  shore  stations  which 
communicate  only  with  other  shore  stations. 

Ship  stations,  and  those  which  communicate  with  ships,  call  and  listen 
for  calls  on  600  and  1000  meters.  The  station  called  when  she  acknowl- 
edges the  call  directs  the  calling  station  what  tune,  as  C  or  D,  to  use  in 
sending,  so  as  to  avoid  interference  with  other  tunes  audible  in  her 
receiver. 

The  above  methods  cannot  be  generally  introduced  until  all  circuits 
on  all  ships  are  properly  calibrated  and  sending  and  receiving  sets  con- 
structed so  as  to  permit  easy,  rapid,  and  definite  changes  of  wave  length 
while  remaining  properly  coupled. 

217.  Whatever  the  speed  of  sending  a  dash  is  equal  in  length  to  three 
dots. 

The  interval  between  two  elements  of  a  letter  is  equal  in  length  to  a  dot. 

The  interval  between  letters  in  a  word  is  equal  in  length  to  a  dash. 

The  interval  between  words  in  a  sentence  is  equal  in  length  to  two 
dashes. 

The  length  of  a  "  space  "  is  two  dots. 

The  long  dash  of  the  letter  L  in  the  American  Morse  equals  two  ordi- 
narv  dashes. 


MANUAL    OF    WIRELESS    TELEGRAPHY. 


163 


TELEGRAPH  CODES. 

ALPHABETS. 


American  Morse. 


Continental  Morse. 


A 

B 

C 

D 

E 

F 

G 

H 

I   . 

J 

K 

L 

M 

N 

O 

P 

Q 

R 

S 

T 

U 

V 

w 

X 
Y 

z 


Wait    

Understand   

Don't  understand 

Call   

Finish 


NUMERALS. 


164 


MANUAL   OF   WIRELESS   TELEGRAPHY. 


TELEGRAPH  CODES.— Continued. 

PUNCTUATIONS,   ETC. 


American  Morse. 


Period    

Colon    

Semicolon 

Interrogation    

Exclamation   

Fraction  line 

Dash   

Hyphen    

Pound  sterling 

Capitalized  letter 

Colon  followed  by  quotation . . . 

Dollar   mark    

Decimal  point 

Comma  

Paragraph   

Underline   (begin)    

Underline  (end)    

Parenthesis    (begin)    

Parqpthesis   (end)    

Quotation  marks   (begin) 

Quotation  marks   (end)    

Quotation    within    a   quotation 

(begin)     

Quotation   within    a   quotation 

(end)    

Apostrophe    


Spell  "  dot  " 


Continental  Morse. 


MANUAL   OF   WIRELESS   TELEGRAPHY. 


165 


COMMON  ABBREVIATIONS. 
[In  use  in  United  States  telegraph  services.] 


Abt  About 

Af  . . After 

Agn Again 

Amn  American 

Amt    Amount 

Anr    Another 

Ar Answer 

Arv    Arrive 

Atk Attack 

Atl    Atlantic 

Awa   Away 

Awi Awhile 

Ax    Ask 

Ay Any 

B  Be 

Bal   Balance 

Bd Board 

Bid   Bundle 

Bf   Before 

Bg Being 

Bn Been 

Bot   Bought 

Bro  Brother 

Bk    Break  or  back 

Bt   But 

Btn Between 

Btr   ...  Better 

Bu    Bushel 

Byd Beyond 

Bz  Business 

Bat   Battery 

Bbl   Barrel 

C   See 

Ca  Came 

Cg Seeing 

Chg Charge 

Cr  Care 

Ct    Connect 

Cty   City 

Cvl    Civil 

Cx Capital  Letter 

Col    Collect 

Ck Check 

Da Day 

Dd Did 

Deg Degree 

Did  Delivered 

Dr Doctor 

Drk Dark 

Dux Duplex 


DH   Deadhead 

Ea    Each 

Ed Editor 

Eng Engine 

Etc   Et  cetera 

Ev Ever 

Evn Even 

Exa    Extra 

Fl    Feel 

Fid   Field 

Fig  Feeling 

Flo    Flow 

Fit Felt 

Fm   From 

Fri    Friday 

Frt    Freight 

Gr Ground 

G.  B.  A Give  better  address 

G.  A Go  ahead 

G.  S.  A Give  some  address 

G.  M Good  morning 

G.  E Good  evening 

G.  N Good  night 

Gen General 

Ger   German 

Gg Going 

Gu Guard 

Gv Give 

Gvg Giving 

Hb Has  been 

Hhd    Hogshead 

Hid Held 

Him    Helm 

Hm  Him 

Hnd    Hundred 

Hon    Honorable 

Hpn    Happen 

Hqrs    Headquarters 

Hr Here 

Hs His 

Hu    House 

Hv    Have 

Hw   How 

Ify    Infantry 

Imp    Import 

Ix    It  is 

Ixu   It  is  understood 

Kp Keep 

Kpg    Keeping 

Kpt Kept 


166 


MANUAL   OF   WIRELESS   TELEGRAPHY. 


COMMON  ABBREVIATIONS.— Continued. 


Kw    Know 

Kwg   Knowing 

Kws    Knows 

Las  Last 

Lat   Latitude 

Lft    Left 

Lit Little 

Lk    Like 

Lt   Lieutenant 

Lv Leave 

Lvg Leaving 

Lvs  Leaves 

Lyg Lying 

Ma May 

Mab    May  be 

Maj Major 

Mar March 

Mas Master 

Mat Material 

Max    Maximum 

Mch Machine 

Mcy    Machinery 

Md    Made 

Mem Member 

Mf  d Manufactured 

Mgr    Manager 

Mh    Much 

Mil    Military       . 

Min    Minute 

Mk    Make 

Mkg   Making 

Mkr    Maker 

Mks Makes 

Mkt    Market 

Ml  Mail 

Mng    Morning 

Mny    Many 

Mo Month 

Mon    Money 

Mrl  Marshal 

Msg    Message 

Msk    Mistake 

Mst    Must 

Mv    Move 

Myn    Million 

Na Name 

Nd    Need 

Nee Necessary 

Neg    Negative 

Ni   Night 

No No,  and  New  Orleans 


Nw   None 

Nv Never 

Nun    Now 

NX Next 

N.  M No  more 

Of c    Officer 

Ofr    Offer 

Of s    Office 

Opr   Operator 

Ot   Out 

Otr    Other 

Ov Over 

O.  K All  right 

PC   Per  cent 

Pd Paid 

Ph Perhaps 

Pha Philadelphia 

Pm    Postmaster 

Po  Post-office 

Pod  Post-Office    Department 

Pot   President  of  the 

Potus   .....  President  of  the  United 

States 

Pr   President 

Pra  Pray 

Prt    Part 

Pt    Present 

Qk Quick 

Qmg Quartermaster-General 

Qr   Quarter 

R Are 

Re  Receive 

Red    Received 

Reg Receiving 

Rcr   Receiver 

Res   Receives 

Ret   Receipt 

Rek Wreck 

Rht Right 

Rlf    Relief 

Rp Report 

Rpt Repeat 

Rr Railroad 

Ru Are  you 

Ruf    Rough 

Ry Railway 

Sa  Senate 

Scotus    Supreme   Court    of   the 

United  States 

Sd  Should 

Sdu  .          . . Sudden 


MANUAL   OF   WIRELESS   TELEGRAPHY. 


167 


COMMON  ABBREVIATIONS.— Continued. 


Sec    Section 

Sed  Said 

Sem    Seem 

Sen  Seen 

Sh Such 

Shf   Sheriff 

Shi    Shall 

Sig   Signature 

Sik   Sick 

Sis    Sister 

Slf Self 

Slo    Slow 

Sir    Sailor 

Sm    Some 

Sma    Small 

Sn  Soon 

Snc Since 

Snd    Send 

Snr   Sooner 

Snt   Sent 

Sor   Soldier 

Sp  Ship 

Spfy   . .  Specify 

Spl    Special 

Spo  Suppose 

Ss   Steamship 

St    Street 

Sta    State 

Stn   Station 

Sto    Store 

Str    Steamer 

Sud Surround 

Sv  Seven 

Svc  Service 

Svd Served 

Sve   Serve 

Svg Serving 

Svl    Several 

Swo    Swore 

Sx  Dollar  mark 

Sy  Say 

S.  Y.  S See  your  service 

T  The 

Tan Than 

Tg Thing 

Tgh Telegraph 

Tgm   Telegram 

Tgr Together 

Tgy Telegraphy 

Th Those 

Thk    ,        ..Thank 


Tho Though 

Thr Their 

Ti    Time 

Tk Take 

Tkg    Taking 

Tkn    Taken 

Tkt  Ticket 

Tlk  Talk 

Tm    Them 

Tn Then 

Tnd Thousand 

Tni   To-night 

Tnk    Think 

Tr  There 

Tru Through 

Ts   This 

Tse These 

Tt   That 

Ttt    That  the  (5) 

Tuf  Tough 

Tw    To-morrow 

Ty They 

U You 

Uc  You  see 

Un Until 

Uni United 

Upn Upon 

Ur  Your 

Urg Urge 

Val   Value 

Vy Very 

W    With 

Wa    Way 

Wat Water 

Wd   Would 

Wea    Weather 

Wg    Wrong 

Wh    Which 

Wi Will 

Wit Witness 

Wl    Well 

Wlk Walk 

Wn    When 

Wnt    Want 

Wo    Who 

Worn Whom 

Wos    Whose 

Wr    Were 

Ws    Was 

Wt What 

Wu   .         . .  Western  Union 


168 


MANUAL   OF   WIRELESS   TELEGRAPHY. 


COMMON  ABBREVIATIONS.— Continued. 


13    Understand 

25    .... I  am  busy  now 

30    No  more 

73    Accept  best  regards 

77    Message  for  you 

92    Deliver 

"  Wire  " — Give  instant  possession 
of  line  for  test. 


An  addition  to  the  foregoing  XX  is  gradually  coming  into  general  use  as 
a  symbol  for  "interference"  which  has  no  counterpart  in  wire  telegraphy. 


Wy   Why 

Y Year 

Ya Yesterday 

4    Please  start  me,  or 

where 

5 Have  you  anything  for 

me 
9    Important   official    mes- 


Chapter  VIII. 

WIRELESS  TELEPHONY. 

WIRELESS   TELEGRAPHY   USING   UNDAMPED  OSCILLATIONS,   DIRECTION 
FINDERS  AND  DIRECTION  SENDERS. 

218.  All  wireless  telephone  sets  thus  far  supplied,  having  proved  unre- 
liable in  action,  have  been  withdrawn  from  service. 

The  workings  of  these  sets  depended  on  the  production  of  undamped 
oscillations  in  the  sending  circuits.  The  apparatus  was  in  principle  like 
that  shown  in  fig.  104,  using  220  volt  direct  current.  The  electrodes  were 
copper  and  carbon  and  the  arc  was  horizontal.  A  small  alcohol  lamp  was 
placed  immediately  under  the  arc  with  its  flame  burning  in  the  arc. 

The  inductance  and  capacity  shunted  around  the  arc  formed  with  it 
an  oscillatory  circuit  similar  to  the  closed  circuit  in  an  ordinary  wireless 
transmitter. 

These  sets  were  used  with  the  ordinary  ship  aerial  tuned  to  the  arc 
circuit.  The  amplitude  of  the  oscillations  induced  in  the  aerial  were 
modified  by  a  carbon  transmitter  in  series  with  the  aerial  as  shown  in 
fig.  105.  Talking  into  the  carbon  transmitter  varied  the  aerial  resistance. 

219.  Assume  that  the   undamped   oscillations   had   a   frequency   of 
700,000  and  the  notes  of  the  human  voice  varied  through  two  octaves 
(say  from  300  to  1200  vibrations  per  second).     The  vibrations  of  the 
telephone  diaphragm  by  changing  the  resistance  of  the  carbon  modified 
the  oscillating  current  in  the  aerial  (and  therefore  the  amplitude  of  the 
electric  waves  generated)  in  accordance  with  the  vibrations  of  the  voice  of 
the  person  speaking.    The  ordinary  receiving  circuit  having  a  crystal  or 
electrolytic   detector  serves  as  well   for  undamped  oscillations  as  for 
groups  of  wave  trains,  transforming  the  modified  oscillations  into  human 
speech  in  the  receiving  telephone. 

The  limit  of  mechanical  or  air  vibrations  recognized  as  sound  is  be- 
tween 30,000  and  40,000  per  second.  Although  the  undamped  oscilla- 
tions are  of  a  much  higher  frequency  and  therefore  produce  no  sound  in 
themselves,  modifications  of  the  amplitude  of  successive  waves  may  be  of 
such  a  nature  as  to  produce  sound  by  slower  variations  in  the  rise  and  fall 
of  the  received  current. 

220.  The  transmitting  telephone  may  be  in  the  arc  circuit  instead  of 
the  aerial  as  shown,  or  it  may  be  inductively  connected  to  either  the  open 
or  closed  circuit.    There  is  as  yet  no  standard  practice.    The  telephone 
transmitters  are  specially  constructed  to  stand  the  voltage  and  current 


170 


MANUAL    OF   WIRELESS    TELEGRAPHY. 


induced  in  the  aerial  or  that  in  the  closed  circuit.  It  is  claimed  that  a 
type  will  soon  be  perfected  that  will  carry  10  amperes. 

It  has  not  been  found  practicable  to  vary  the  arc  current  sufficiently  to 
produce  large  powers  in  the  oscillating  circuits.  Arcs  in  parallel  and  in 
series  have  been  tried  but  without  marked  success. 

221.  The  arc  method  of  producing  undamped  oscillations  with  direct 
current  was  discovered  by  Professor  Elihu  Thompson  in  1892  and  has 
been  developed  by  many  other  investigators.  In  order  to  prevent  the 
oscillations  from  running  back  to  the  dynamo  choke  coils  or  very  high 
resistances  must  be  placed  in  the  D.  C.  leads.  (See  figs.  104  and  105.) 

The  simple  theory  of  the  formation  of  the  oscillations  is  as  follows : 

When  the  shunt  containing  inductance  and  capacity  is  closed  around 
the  arc  in  a  circuit  like  that  shown  in  fig.  104,  a  part  of  the  current  flows 

RESISTANCE 


CHOKE    COIL. 

FlG.    104. 

into  the  condenser,  thus  robbing  the  arc  of  a  part  of  its  current;  but  as 
the  D.  C.  potential  across  an  arc  increases  as  the  current  decreases,  this 
decrease  in  current  increases  the  potential  difference,  and  the  condenser 
continues  to  charge.  At  the  next  instant,  however,  the  condenser  com- 
mences to  discharge,  increasing  the  direct  arc  current  until  it  is  entirely 
discharged;  then  the  process  repeats  itself. 

Oscillations  can  be  produced  in  this  way  from  almost  any  form  of  arc 
and  over  a  wide  range  of  voltages,  but  it  is  found  that  high  frequency 
oscillations  are  best  produced  when  the  direct  current  voltage  is  high 
(500  volts  or  more),  and  when  the  positive  arc  electrode  is  capable  of 
conducting  away  heat  rapidly.  This  rapid  cooling  of  the  arc  plays  a 
very  important  part  in  the  production  of  the  oscillations,  as  it  causes  the 
arc  to  die  down  rapidly  and  increases  the  suddenness  with  which  the 
current  flows  into  the  condenser.  It  has  also  been  found  that  when  the 
arc  is  formed  in  an  atmosphere  capable  of  assisting  in  this  cooling,  the 
energy  of  the  oscillations  is  vastly  increased.  The  best  gaseous  conductor 
of  heat  is  hydrogen,  and  consequently  the  best  results  are  obtained  in  an 
atmosphere  of  hydrogen  or  some  mixed  gas  or  vapor  containing  hydrogen. 
Common  illuminating  gas  gives  excellent  results,  and  recently  alcohol 


MANUAL    OP    WIRELESS    TELEGRAPHY. 


171 


introduced  into  the  arc  chamber  drop  by  drop  and  vaporized  by  the 
heat  of  the  arc  has  come  into  use.  It  has  been  suspected  that  these 
gases  and  vapors  may  have  some  effect  on  the  electrical  conductivity  of 
the  arc  as  well  as  on  its  cooling,  but  this  point  is  still  unsettled. 

222.  Another  device  which  is  made  use  of  for  increasing  the  energy 
of  the  oscillations  which  can  be  obtained  from  the  arc  is  forming  it  in 
a  magnetic  field  the  lines  of  force  of  which  are  at  right  angles  to  the 
arc  length.  The  action  of  the  magnetic  field  is  twofold;  first  it  deflects 
the  arc  to  one  side,  increasing  its  length  and  consequently  the  difference 
of  potential  between  the  arc  electrodes,  and  second,  it  blows  out  of  the 
field  the  conducting  ions  formed  in  the  gas,  thus  decreasing  the  arc 
conductivity  and  still  further  increasing  the  difference  of  potential  be- 
tween the  electrodes. 


PILOT  LAMP 


FIG.  105. 


For  the  successful  production  of  oscillations  a  correct  relation  must 
exist  between  the  arc  current,  the  arc  length,  and  the  strength  of  the 
magnetic  field.  This  relation  in  general  can  be  obtained  only  by  ex- 
periment. If  these  adjustments  are  not  correctly  made  several  sets  of 
useless  superposed  oscillations  may  be  produced  in  the  condenser  circuit. 
Therefore  it  is  necessary  in  working  with  waves  produced  from  the  arc 
to  examine  its  oscillations  from  time  to  time  with  the  wave  meter,  in 
which,  if  the  adjustment  be  correct,  but  one  sharp  and  powerful  maxi- 
mum will  be  found. 

Fleming  states  that  the  best  results  are  obtained  when  the  ratio  of  the 
capacity  to  the  inductance  in  the  oscillating  circuit  is  small — about  1  to 
20 — when  both  are  measured  in  centimeters. 
12 


MANUAL    OF    WIRELESS    TELEGRAPHY. 

223.  Fessenden  has  developed  another  means  of  producing  undamped 
oscillations  by  constructing  alternators  giving  as  high  as  150,000  alter- 
nations per  second.     The  open  circuit  is  connected  directly  to  the  ter- 
minals of  these  alternators  and  tuned  to  the  alternator  frequency.    The 
use  of  these  very  high  frequency  alternators  does  away  with  all  trans- 
formers, condensers  and  inductances  except  the  aerial  tuning  inductance. 
They  are,  however,  not  yet  in  general  use,  being  difficult  to  construct  and, 
on  account  of  their  high  speed,  difficult  to  operate. 

They  are  suitable  for  either  wireless  telephony  or  telegraphy. 

224.  The  advantage  to  be  derived  from  the  use  of  undamped  oscilla- 
tions is  considerable.    We  have  forms  of  wireless  detectors,  like  the  elec- 
trolytic and  perikon  receivers,  which  respond  in  proportion  to  the  total 
energy  passing  through  them.    Detectors  of  this  kind  will  give  the  same 
response  whether  the  energy  is  introduced  in  the  form  of  an  undamped 
continuous  train  of  small  amplitude  or  a  damped  train  consisting  of  a 
few  waves  some  of  which  are  of  large  amplitude.    The  undamped  waves 
offer  great  advantages  in  the  way  of  sharp  tuning,  and  enable  the  receiv- 
ing circuits  to  be  so  set  up  that  they  may  be  made  comparatively  free 
from  the  interference  from  other  stations  and  from  atmospheric  dis- 
turbances. 

The  advantages  at  the  sending  stations  are  no  less  important,  for  there, 
with  the  high  potentials  used  in  a  spark  circuit,  a  considerable  portion 
of  the  energy  is  wasted  on  account  of  brush  discharges  in  the  condensers 
and  in  other  portions  of  the  circuit,  and  on  account  of  leakage  due  to 
faulty  insulation.  With  the  undamped  oscillations  these  difficulties  prac- 
tically disappear,  for  with  maximum  potentials  not  exceeding  1000  volts 
in  the  primary  circuit,  an  amount  of  energy  can  be  transmitted  to  the 
antenna  which  would  with  the  spark  circuit  require  potentials  of  30,000 
or  more  volts.  It  is  also  claimed  for  the  undamped  oscillations  that  they 
travel  over  rough  and  broken  country  with  much  less  absorption  than  is 
found  in  the  case  of  the  ordinary  spark  waves,  but  in  regard  to  this  and 
many  other  questions  concerning  the  qualities  of  undamped  oscillations 
we  must  wait  for  confirmation  until  they  come  into  more  general  use. 

In  using  undamped  oscillations  for  wireless  telegraphic  purposes  it 
must  be  remembered  that  the  frequency  of  the  oscillations  themselves  is 
too  high  to  be  heard  in  the  telephone  connected  with  the  ordinary  re- 
ceiving circuit,  and  when  the  circuit  at  the  sending  station  is  closed  all 
that  would  be  heard  is  a  slight  click,  so  that  there  is  no  way  of  telling  a 
dot  from  a  dash.  This  makes  it  necessary  to  place  a  rapidly  rotating 
circuit  breaker  in  the  circuit  for  the  purpose  of  creating  a  buzz  in  the 
telephone  at  the  receiving  station  when  the  circuit  is  closed.  This  circuit 
breaker  is  ordinarily  placed  in  the  aerial,  while  the  sending  key  is  placed 
either  in  the  aerial  or  shunted  around  a  few  turns  of  the  aerial  induc- 
tance, in  which  case  it  serves  merely  to  throw  the  aerial  in  and  out  of 
tune  with  the  closed  circuit. 


MANUAL    OF    WIRELESS    TELEGRAPHY. 


173 


THE   POULSEN   TICKER  RECEIVER    FOR   UNDAMPED  OSCILLATIONS. 

225.  If  no  interrupter  is  used  in  the  sending  apparatus  for  undamped 
oscillations,  no  signals  can  be  read  at  a  receiving  station  unless  the  wave 
trains  are  there  broken  up  so  as  to  produce  a  buzz  in  the  telephone.  For 
this  purpose  the  Poulsen  ticker  is  sometimes  used,  which,  at  the  same 
time  does  aAvay  with  the  need  of  any  special  receiver.  It  consists  essen- 
tially of  a  circuit  breaker  actuated  by  a  small  magnetic  vibrator,  kept  in 
action  by  a  dry  cell.  In  this  receiver  the  closed  circuit  is  coupled  very 
loosely  to  the  antenna  (see  fig.  106),  and  this  circuit  is  intermittently 


FIG.  106. 


connected  to  a  large  condenser  K,  of  the  order  of  a  microfarad,  by  the 
ticker  at  A. 

During  the  time  of  contact  the  condenser  K  becomes  charged,  and 
when  the  contact  is  broken  it  discharges  itself  through  the  telephone, 
producing  a  note  corresponding  in  tone  to  the  frequency  of  the  ticker. 

DIRECTION   FINDERS. 

226.  The  experimental  installations  of  direction  finders  have  been  with- 
drawn, it  not  being  found  practicable  to  operate  them.  The  principle  on 
which  they  operated  was  that  two  vertical  wires  parallel  to  the  plane  of 
movement  of  an  electric  wave,  if  half  a  wave  length  apart,  would  have 
electric  currents  of  opposite  phase  induced  in  them,  which  could  be  made 
to  double  the  receiving  effect  as  compared  with  a  single  wire,  while  if  at 
right  angles  to  the  plane  of  movement  of  the  wave,  the  induced  currents 
would  be  in  the  same  direction  and  could  be  made  to  neutralize  each 
other.  If  the  plane  of  this  direction  finder  pointed  towards  the  sending 
station,  the  strength  of  the  received  signals  would  be  a  maximum.  If  at 
right  angles  to  the  sending  station,  it  would  be  a  minimum. 

By  swinging  the  ship  in  azimuth,  the  compass  heading,  when  the 
strength  of  signal  was  a  maximum,  would  indicate  the  line  of  bearing  of 
the  sending  station.  The  practical  difficulty  in  the  way  of  operating  this 
system  to  the  best  advantage  is  the  very  short  waves  which  are  necessary 
on  account  of  the  comparatively  short  distances  that  can  be  obtained  be- 
tween wires  on  board  ship.  For  instance,  with  masts  200  feet  apart  the 


174  MANUAL   OF    WIRELESS    TELEGRAPHY. 

wave  length  should  be  400  feet,  whereas  the  navy  standard  wave  length  is 
1275  feet,  The  plane  of  such  an  aerial  relative  to  the  direction  of  the 
electric  waves  makes  a  difference  in  the  strength  of  received  signals 
whether  the  distance  between  wires  is  half  a  wave  length  or  not.  And  this 
fact  is  utilized  in  the  Bellini-Tosi  apparatus  where  two  such  aerials  are 
installed  (see  fig.  63)  in  planes  at  right  angles  to  each  other.  The  open 
circuit  receiving  coils  are  mounted  so  that  they  are  in  the  same  planes  as 
their  aerials.  The  closed  circuit  coil  can  be  placed  in  the  plane  of  either 
aerial  or  in  any  intermediate  position.  Its  plane  when  the  strength  of 
signals  is  a  maximum  is  approximately  that  of  the  passing  waves. 

227,  ~No  attempt  to  send  directed  waves  from  ships  has  been  made. 

On  shore,  direction  finders  can  be  more  successfully  used  than  on  ships. 

It  is  found  by  Marconi  that  a  flat  top  aerial  like  fig.  64  sends  more 
strongly  in  the  direction  away  from  the  free  end  of  the  aerial  and  re- 
ceives more  strongly  from  the  direction  in  which  it  sends  the  best.  This 
effect  with  the  comparatively  short  horizontal  part  of  the  aerial  on  ships 
is  not  appreciable,  but  on  shore  where  the  horizontal  part  can  be  made 
long  as  compared  with  the  vertical  part  it  has  proved  to  be  of  practical 
use,  both  as  a  direction  sender  and  receiver.  The  trans- Atlantic  wireless 
stations  at  Clifden  and  Glace  Bay  have  their  aerials  pointing  away  from 
each  other.  To  be  used  as  a  direction  finder  such  an  aerial  would  have 
to  be  revolved  rapidly  or  the  horizontal  part  extended  in  a  number  of 
directions  like  the  spokes  of  a  wheel,  to  any  one  of  which  the  vertical 
part  could  be  connected  at  will. 

PORTABLE    SETS. 

228.  These,  as  their  name  indicates,  are  special  small  sets  which  have 
their  own  source  of  power,  such  as  a  foot  or  hand  operated  generator,  and 
when  used  on  shore  have  portable  masts  for  supporting  the  aerial.     On 
board  ship  this  single  wire  aerial  can  be  run  up  by  signal  halliards,  and  if 
insulated  wire  is  used  (since  portable  sets  work  usually  at  low  voltages) 
no  particular  care  need  be  taken  to  prevent  the  wire  from  touching  the 
mast,  deck  or  rigging. 

The  suit-case  type  illustrated  in  fig.  107  weighs  about  75  pounds  com- 
plete. It  has  a  motor  generator  for  ship  use,  which  has  an  output  of  50 
watts  and  can  be  plugged  in  on  any  lighting  circuit.  Small  gasolene 
driven  generators  are  used  for  some  portable  shore  sets,  the  entire  send- 
ing and  receiving  apparatus  being  mounted  on  wheels.  The  power  or 
hand  operated  generator  set  of  the  suit-case  type  is  good  for  about  20 
miles.  (See  fig.  107.)  A  complete  set  is  seen  with  condenser,  inductance, 
and  key  in  the  left  half;  motor  generator,  quenched  gap,  transformer, 
and  receiving  apparatus  on  the  right  half  of  the  case ;  with  the  plug  for 
connecting  up  with  the  lighting  or  power  circuit  at  the  upper  left  hand 
corner. 


MANUAL   OF   WIRELESS    TELEGRAPHY.  175 

229.  To  illustrate  an  actual  wireless  telegraph  installation  the  station 
at  Sitka,  Alaska,  has  been  selected.  This  station  is  situated  on  Japonski 
Island  (see  frontispiece).  The  masts,,  rigging  and  rigging  insulators, 
aerial  and  buildings  are  shown  in  fig.  108 ;  one  unit  of  the  generating 
sets  in  fig.  109;  the  receiving  apparatus  in  fig.  110.  These  figures  repay 
study  as  illustrating  a  neat  and  workmanlike  installation.  The  sending 
and  receiving  apparatus  is  after  the  designs  of  Professor  Pierce. 


FIG.  107. — N.  E.  S.  Co.'s  Portable  Set  Signal  Corps. 

Figs.  Ill  and  Ilia  illustrate  actual  receiving  sets  of  other  types,  the 
elementary  diagrams  of  which  are  shown  in  figs.  83  and  86. 

The  construction  and  arrangement  of  both  sending  and  receiving 
apparatus  will  continue  to  vary,  but  a  careful  study  of  elementary  dia- 
grams (figs.  40  to  48  and  77  to  88)  in  connection  with  installation  dia- 
grams like  figs.  112,  112a,  112b,  112c,  which  accompany  each  set  will 
enable  an  electrician  to  connect  up  and  operate  any  set  intelligently. 
There  are  too  many  types  of  apparatus  in  use  to  warrant  a  detailed 
description  or  illustration  of  each.  Such  description  and  instructions  are 
furnished  with  each  set.  This  manual  has  therefore  been  confined  to  the 
principles  common  to  practically  all  wireless  sets. 


176 


MANUAL    OF   WIRELESS    TELEGRAPHY. 


MANUAL   OF    WIRELESS    TELEGRAPHY. 


177 


178 


MANUAL    OF    WIRELESS    TELEGRAPHY. 


FIG.  110. 


MANUAL    OF    WIRELESS    TELEGRAPHY. 


179 


FIG.  111. — Wireless  Telegraph  Receiver. 


180 


MANUAL   OF   WIRELESS   TELEGRAPHY. 


TETLEFUNKEN. 

FIG.  112. 


TO  AERIAL 


HOT  WIRE  AMM. 


SHIP  MAINS 


CLOSED  CIRCUIT  OPEN  CIRCUIT 

INDUCTANCE.  INDUCTANCE 


FESSELNDEM  . 

FIG.  112A. 


MANUAL   OF   WIRELESS   TELEGRAPHY. 


181 


182 


MANUAL   OP  WIRELESS   TELEGRAPHY. 


MANUAL   OF   WIRELESS   TELEGRAPHY.  183 

STATIC   AND   PREVENTION   OF   INTERFERENCE. 

230.  Methods  of  preventing  interference  by  the  use  of  standard  calling 
wave  lengths  and  codified  standard  communicating  wave  lengths  were 
referred  to  under  codes  (art.  216).  The  use  of  undamped  oscillations 
would  materially  assist  in  the  sharp  tuning  necessary  to  accomplish  the 
above  successfully ;  but  neither  undamped  nor  damped  oscillations  can  be 
relied  upon  to  completely  eliminate  the  effects  of  the  vagrant  waves  and 
local  electrification  grouped  under  the  name  of  "  static." 

Every  lightning  discharge  produces  powerful  electric  waves  which 
affect  conductors  at  great  distances,  and  since  thunderstorms  in  warm 
climates,  and  especially  in  summer,  are  almost  continuous  in  the  sense 
of  existing  somewhere  in  the  area  in  which  they  affect  detectors,  the 
interference  caused  by  them  is  almost  continuous. 

The  waves  created  by  lightning  discharges  vary  greatly  in  length;  but 
are  highly  damped  and  affect  all  aerials  more  or  less.  Again,  at  every 
wireless  station  the  air  at  the  top  and  foot  of  the  aerial  is  at  different 
potentials.  The  atmospheric  potential  gradient  at  any  station  varies 
with  the  time  of  day,  the  season  of  the  year,  and  the  local  weather  con- 
ditions. It  is  usually  steeper  in  summer. 

This  difference  of  potential  tends  to  equalize  itself  through  the  aerial. 

The  upper  air  is  usually  positively  electrified,  the  earth  negatively. 

The  amount  and  regularity  of  the  discharge  to  ground  at  any  time 
depend  on  the  difference  of  potential  between  the  upper  air  and  the 
ground  at  the  time  and  the  amount  of  electrified  air  which  comes  in 
contact  with  the  aerial. 

The  discharges  are  usually  intermittent  and  vary  in  strength.  Some- 
times they  produce  a  continuous  roar  in  the  telephone. 

In  this  respect  the  note  of  the  spark  affects  reception  and  it  is  possible 
to  read  a  500-cycle  note  through  static  which  would  render  a  60-cycle 
note  unintelligible. 

Whatever  tends  to  selectivity  or  inertia  in  receiving  circuits,  such  as 
large  inductances,  also  tends  to  decrease  static  interference. 

Inductively  coupled  receiving  sets  afford  a  direct  path  to  ground,  so 
that  static  charges  do  not  accumulate  on  the  aerial,  and  the  inductive 
coupling  weakens  the  energy  transfer  of  all  induced  currents  which  are 
out  of  tune. 

We  see  therefore  that  loose  coupling,  small  damping  and  high  fre- 
quency, which  we  desire  for  other  reasons,  are  also  desirable  as  tending 
to  eliminate  static  interference. 


APPENDICES. 


NOTE  1. 

The  following  list  of  metals  is  arranged  in  such  order  that  any  one  will 
be  the  positive  pole  of  the  battery  when  used  with  the  metal  next  below  it 
on  the  list  as  a  battery  element  and  the  negative  pole  when  used  with  the 
element  next  above  it,  the  difference  of  potential  between  any  two  being 
greater  the  farther  apart  they  are  in  the  series. 

Carbon.  Silver.  Lead.  Zinc. 

Platinum.  Copper.  Cadmium.  Magnesium. 

Gold.  Iron.  Tin.  Sodium. 

The  amount  of  potential  difference  also  depends  on  the  battery  solution, 
and  in  some  instances  it  may  be  reversed.  Commercial  primary  batteries  are 
of  copper  and  zinc,  with  an  E.  M.  F.  of  approximately  1  volt,  and  carbon  and 
zinc,  with  an  E.  M.  F.  of  from  1.4  in  Leclanche  cells  and  some  dry  cells  to 
2.1  in  some  types  of  wet  cells,  depending  on  the  electrolyte. 

NOTE  2. 

The  relations  existing  between  electricity  and  matter  have  been  most  ex- 
haustively investigated  by  Prof.  J.  J.  Thomson,  who  has  proved  that  electric- 
ity has  an  atomic  structure  and  that  it  can  exist  separately  from  an  atom 
of  matter. 

When  a  current  is  sent  through  a  vacuum  tube,  the  luminous  beam  pro- 
ceeding from  the  cathode  has  been  shown  to  consist  of  particles  projected 
from  the  cathode.  These  particles  are  capable  of  turning  a  small  wheel. 
The  cathode  beam  can  be  deflected  by  either  a  magnetic  or  an  electric  field, 
and  it  is  found  to  consist  of  particles  of  negative  electricity  or  of  parts  of 
the  atom  negatively  charged,  each  having  about  one-thousandth  of  the  mass 
of  an  atom  of  hydrogen. 

These  particles  are  the  same,  no  matter  what  gas  is  used  in  the  vacuum 
tube.  They  are  usually  called  electrons.  When  an  electron  is  broken  off 
from  an  atom,  the  remaining  part  is  positively  charged.  Currents  of  elec- 
tricity, however  produced,  are  the  result  of  the  decomposition  of  atoms  into 
positive  and  negative  electric  charges.  There  can  be  no  electric  current 
without  movement  of  electrons.  Conductors  are  bodies  in  which  the  break- 
ing up  of  atoms  and  movements  of  electrons  take  place  more  or  less  easily. 
Some  free  electrons  exist  in  all  bodies.  It  is  by  setting  these  into  vibration 
and  by  means  of  this  vibration  making  them  break  off  similar  particles  from 
neighboring  atoms,  and  thus  propagate  the  disturbance  throughout  the  mass 
of  the  conductor,  that  electric  currents  are  generated. 


186  APPENDICES. 

APPENDIX  A. 

TABLE  1. 

[Extract  from  Fleming's  Cantor  lecture,  Journal  of  Society  of  Arts,  p.  196, 
January  5,  1906.  Taken  mostly  from  A.  Heydweiller,  "  On  Spark  Poten- 
tials." Ann.  der  Physik,  vol.  248,  p.  235  (1898).] 

SPABK  VOLTAGE  BETWEEN  BRASS  BALLS  2  CENTIMETERS  IN  DIAMETER  FOR 
VARIOUS  SPARK  LENGTHS. 

Spark  length  (cms.).  voFtag*.                      SPark  len*th  (cm8')'              voltage. 

0.1 4,700  1    31,300 

0.2 8,100  1.5 40,300 

0.3 11,400  2 47,400 

0.4 '. 14,500  2.5 53,000 

0.5 17,500  3    57,500 

0.6 20,400  3.5 61,100 

0.7 23,250  4    64,200 

0.8 26,100  4.5 67,200 

0.9 28,800  5    69,800 


TABLE  2. 

Condenser  Capacity  Required  to  Give  Full  ana-,r  ,-r.n-a.ro 

Power  for  Spark  Voltage  of  30.000  (0.4"  Gap)  bp  of  U  000 

K.  W.                                 and  One  Discharge  Per  Half  Cycle.  (0 15"  gap). 

r60  cycles.           120  cycles.       "~460  cycles?  500  cycles. 

1   0.019m.  f.         0.009m.  f.         0.002  m.  f.  0.010  m.  f. 

2} 0.047     "            0.023     "            0.006     "  0.025     " 

5   0.09a     "            0.047     "            0.012     "  0.050     " 

10   0.185     "            0.093     "            0.024     "  0.100     " 

15  0.27&    "           0.139     "           0.036     "  0.150     " 

35  0.648     "            0.324     "            0.085    •"  0.350  •." 

1  standard  jar  condenser  =  0.002  m.  f. 

microfarads  X  spark  voltage  X  spark  voltage  X  spark  frequency 


K.W.  = 


2,000,000,000 


TABLE  3. 

INCREASE  OF  RESISTANCE  OF   COPPER  WIRE  AT  A  FREQUENCY  OF  400,000  PEK 
SECOND  (750  METER  WAVE  LENGTH). 

Diameter  Increase 

of  wire.  in  resistance. 

0.2  mm.  1  per  cent. 

0.4     "  22 

0.8     "  120 

2.0     "  650 

4.0     "  1000 


APPENDICES.  187 

TABLE  4. 
SPECIFIC  RESISTANCE  OF  WATER  AND  SOILS. 

Sea  water   100 

Fresh  water    100,000 

Damp  soil 10,000  —  100,000 

Dry  soil   >1,000,000 


TABLE  5. 

LOGARITHMIC  DECREMENT  (8)   OF  WAVE  TRAIN  AND  THE  APPROXIMATE  NUMBER 

OF  WAVES   (N.)  IN  THE  TRAIN  BEFORE  THE  AMPLITUDE  FALLS 

TO    ONE-TENTH    OF    THE   MAXIMUM. 

5  N                                          5  N 

1.0  3.5  .1  24.0 

0.8  4.0  .08  30.0 

.6  5.0  .06  39.0 

.4  7.0  .04  58.0 

.3  8.5  .03  78.0 

.2  12.5  .02  116.0 

Good  tuning  is  not  possible  with  less  than  fifteen  waves  in  the  train. 


TABLE  6. 
SOME  COMMON  UNITS  EXPRESSED  IN  TERMS  OF  ABSOLUTE  UNITS. 

1  microfarad  =  1  .  10-is  c.  g.  s. 

1  millihenry  =  1  .  10«       " 

1  microhenry  =  1  .  10s       " 

1  volt  =  1  .  10s 

1  ohm  =  1  .  10» 

1  ampere  =  1  .  10-i     " 

1  watt  =  1  .  107 

TABLE  7. 

SOME  COMMON  HIGH-FREQUENCY  EQUATIONS. 
The  time  of  oscillation  of  a  condenser  circuit  is 

T  =  2 TT  */ LC  seconds. 
(L  in  henries,  C  in  farads.) 

1 

v  =  n'k  and  T •=.  —  , 
n 

where  v  is  the  velocity,  n  the  frequency,  and  X  the  wave  length. 
The  wave  length  is  therefore 

/,  m:  V   .    &TC  ^/    AJ\J) 

A  =  1.885  */LC~  .109  meters. 
13 


188  APPENDICES. 

In  a  condenser  charged  N  times  per  second  the  energy  passing  through  in 

watts. 


one  second  is 

.   CF2 


(C  in  microfarads  and  V  in  volts.) 
The  damping  of  a  single  circuit  is 


(R  in  ohms  and  L  in  henries  or  both  in  absolute  units.) 
The  damping  of  two  circuits  by  the  resonance  method, 


or 


See  art.  208. 

The  following  equation  and  tables  are  the  results  of  experiments  conducted 
between  Brant  Rock  station  and  the  cruisers  Salem  and  Birmingham  in 
1909-10.  See  "  Some  Quantitative  Experiments  in  Long  Distance  Radio- 
Telegraphy,"  by  L.  W.  Austin,  Reprint  No.  159,  from  Bulletin  Bu.  of  Stand- 
ards, Vol.  7,  No.  3,  Feb.  1,  1911. 

Equation:    IR  —  4.25  x  Is  x *— —  x  e~   ^ 

Is  =  Antenna  current,  sending,  in  amperes. 
IR  =  Antenna  current,  receiving,  amperes  through  25  ohms. 
7i,  =  Height  of  flat-top  antenna,  sending  station,  in  kilometers. 
A2  —  Height  of  flat-top  antenna,  receiving  station,  in  kilometers. 

a  =  .0015. 

d  =  Distance  in  kilometers. 

/.  —  Wave  length  in  kilometers. 

«=  2.7183. 


25  ohms  =  high-frequency  resistance  of  ship  aerial  of  1000-meter  wave 
length. 

The  above  equation  covers  the  normal-day  received  current  over  salt  water, 
through  25  ohms  for  two  stations  with  flat-top  aerials  of  any  height,  with  any 
value  of  sending  current  and  any  wave  length,  provided  the  sending  station 
is  so  coupled  as  to  give  but  one  wave  length. 

The  following  tables  (8,  9,  10  and  11,  12)  illustrate  the  application  of  this 
equation: 

TABLE  8. 

For  good  communication  received  current  should  be  equal  to  7^  =  40  X  10-« 
amperes  through  25  ohms  =  40  X  10-s  watts  =  ^  erg  per  second. 

For  auditle  signals  7^  =  10  X  10-«  amperes  through  25  ohms  =  2.5  X  10-» 
watts  =  ¥V  erS  Per  second. 


APPENDICES. 


189 


TABLE  9. 

Calculated  Relation  between  Antenna  Current  and  Distance  for  Two  Ships  with 

Antenna  Heights  of  130  Feet. 

A  =  lOOOm. 


Antenna  Current 
Is- 

Working  Distance 
40.10-«  amp. 

Extreme  Distance  of  Audibility 
10.  10-6  amp. 

Day. 

Night. 
(Zero  Absorption) 

Day. 

Night. 
(Zero  Absorption) 

1  amp. 

75  miles 

90  miles 

200  miles 

360  miles 

2 

135 

180 

300 

720 

3 

180 

270 

375 

1080 

5 

235 

450 

475 

1800 

7 

280 

630 

550 

2520 

10 

345 

900 

630 

3600 

15 

420 

]350 

725 

5400 

20 

475 

1800 

790 

7200 

25 

525 

2250 

840 

9000 

30 

565 

2700 

900 

10800 

40 

630 

3600 

970 

14400 

50 

685 

4500 

1025 

18000 

60 

725 

5400 

1150 

21600 

TABLE  10. 

Good  Working  Distance  and  Sending  Current  for  Two  Stations  with  Flat-Top  Antennas 

450  Feet  High. 


Nautical  Miles. 

A  =  1000  m. 

A  =  2500  m. 

A  =  3750  m. 

A  =  6000m. 

1000 

15  amp. 

13.5  amp. 

15  amp. 

17  amp. 

1250 

38 

27 

27 

30 

1500 

91 

49 

44 

46 

1750 

200 

95 

77 

74 

2000 

490 

155 

122 

105 

2250 

245 

200 

160 

2500 

... 

470 

314 

235 

2750 

... 

500 

335 

3000 

... 

... 

775 

500 

190 


APPENDICES. 


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APPENDICES.  191 

APPENDIX  B. 

1.  The  facilities  of  the  naval  coastwise  wireless  telegraph  stations  (includ- 
ing the   one  on   the  Nantucket   Shoal   light-ship),   for  communicating  with 
ships    at    sea,    where    not    in    competition    with    private    wireless    telegraph 
stations,  are  placed  at  the  service  of  the  public  generally  and  of  maritime 
interests  in  particular  under  rules  which  are  subject  to  modification  from 
time  to  time,  for  the  purpose  of — 

(a)  Reporting  vessels  and  intelligence  received  by  wireless  telegraphy  with 
regard  to  maritime  casualties,  derelicts  at  sea,  and  overdue  vessels. 

(ft)  Receiving  wireless  telegrams  of  a  private  or  commercial  nature  from 
ships  at  sea,  for  further  transmission  by  telegraph  or  telephone  lines. 

(c)   Transmitting  wireless  telegrams  to  ships  at  sea. 

2.  For  the  present,  this  service  will  be  rendered  free.     All  messages  will, 
however,  be  subject  to  the  tariffs  of  the  land  lines.    Arrangements  have  been 
made  with  both   the  Western  Union   and   Postal   Telegraph  companies  for 
forwarding  messages  received  from  ships  at  sea.    When  a  message  is  not  pre- 
paid the  company  delivering  it  will  collect  the  charges.     Shipowners  should 
arrange  with  companies  operating  the  land  lines  as  to  tariffs  and  the  settle- 
ment therefor. 

3.  The  light-ship  stations  will  report  vessels  and  transmit  messages  from 
them  if  the  signals  are  made  by  the  international  code  or  any  other  known 
to  the  officers  on  the  light-ship. 

4.  When  notified  by  the  Weather  Bureau  of  the  Department  of  Agriculture, 
naval  wireless  telegraph  stations  will  give  storm  warnings  to  vessels  com- 
municating with  them  by  wireless  telegraphy.     Storm  warnings  will  be  sent 
to  the  light-ships  by  wireless  telegraphy,  and  storm  signals  furnished  by  the 
Weather  Bureau  will  be  displayed  therefrom  to  warn  passing  vessels.    Storm 
warnings   and  hydrographic  information,   such  as  location  of  derelicts  and 
other  dangerous  obstructions  to  navigation,  are  sent  broadcast  at  8  A.  M., 
noon  (immediately  after  noon-time  signal),  4  P.  M.  and  8  P.  M.  local  standard 
time  when  received.    Weather  reports  and  other  hydrographic  information  on 
file  are  furnished  on  request. 

5.  All  vessels  having  the  use  of  the  n^val  wireless  telegraph  service  are 
requested   to   take   daily   meteorological7 observations   of   the   weather   when 
within    communicating    range    and    to    transmit    such    observations    to    the 
Weather  Bureau   by  wireless  telegraphy  at   least  once  daily,   and  transmit 
observations  oftener  when  there  is  a  marked  change  in  the  barometer. 

6.  All  shipowners  desiring  to  use  any  special  code  of  signals  for  communi- 
cating  with    the   Nantucket   Shoal   light-ship    station    or   any    of   the    shore 
stations,  or  make  any  other  special  arrangements,  should  communicate  with 
the  Navy  Department,  Washington,  D.  C. 

7.  All    chambers    of    commerce,    maritime    exchanges,    newspapers,    news 
agencies,  and  others  desiring  to  have  vessel  reports  and  general  marine  news 
forwarded   to   them   regularly  should   communicate   with  the  Navy   Depart- 
ment   in    order    that    necessary    arrangements    for    the    service    may    be 
made.     In  no  case  will  an  operator  attached  to  a  station  be  allowed  to  act 
as  an  agent  for  any  individual  or   corporation,  but  all  vessel  reports  and 
marine  news  not  of  a  private  nature  will  be  supplied  to  all  applicants,  so 
long  as  this  service  does  not  too  greatly  tax  the  personnel  of  the  stations, 
when   it  will  be   necessary  for  those  desiring  information   involving  much 
time  for  its  distribution  to  appoint  agents,  who  will  be  allowed  access  to  the 
station  bulletins. 


192  APPENDICES. 

8.  Naval  wireless  telegraph  stations  are  equipped  with  apparatus  of  several 
systems  and  can  communicate  with  all  the  wireless  telegraph  systems  now 
in  use,  if  tuned  to  the  same  wave  length.  The  Department  is  desirous  of 
co-operating  with  all  shipowners  wishing  to  avail  themselves  of  its  wireless 
telegraph  service,  and  it  is  believed  that  there  will  be  little  or  no  difficulty 
in  arranging  for  communication  between  its  stations  and  ships  equipped  with 
apparatus  of  other  systems,  if  the  owners  of  the  apparatus  as  well  as  the 
owners  of  the  ships  are  desirous  of  establishing  such  communication. 

INSTRUCTIONS  FOR  COMMUNICATION  BY  WIRELESS  TELEGRAPHY  BETWEEN  WIRELESS 
TELEGRAPH  STATIONS  AND  SHIPS. 

I.  A  vessel  wishing  to  communicate  with  a  station  and  having  ascertained 
by  "  listening  in  "  that  she  is  not  interfering  with  messages  being  exchanged 
within  her  range  should  make  the  call  letter  of  the  station. 

II.  The  call  should  not  be  continuous,  but  should  be  at  intervals  of  about 
three  minutes  in  order  to  give  the  station  a  chance  to  answer. 

III.  After  the  station  answers  the  vessel  should  send  her  name,  distance 
from  station,  weather,  and  number  of  words  she  wishes  to  send;   then  stop 
until  the  station  makes  O.  K.,  signals  the  number  of  words  she  wishes  to 
send  to  vessel,  and  signals  go  ahead. 

IV.  Then  the  vessel  begins  to  send  her  messages,  stopping  at  the  end  of 
each  50  words  and  waiting  until  the  station  signals  O.   K.  and  go   ahead; 
when  all  messages  have  been  sent  she  will  so  indicate.     If  the  sender  desires 
to    designate    the   Western    Union   or    Postal   Telegraph    system   for   further 
transmission  of  his  message,  he  should  do  so  immediately  after  the  address, 
as,  for  example  "  A.  B.  C.,  Washington,  D.  C.,  via  W.  U.  (or  P.  T.)." 

V.  When  a  vessel  has  indicated  that  she  has  finished,  the  station  will  send 
to  the  vessel  such  messages  as  she  may  have  for  her  in  the  following  order: 

(a)  Government  business,  viz.,  telegrams  from  any  Government  Depart- 
ments to  their  agents  on  board. 

(&)  Business  concerning  the  vessel  with  which  communication  has  been 
established,  viz.,  telegrams  from  owner  to  master. 

(c)  Urgent  private  dispatches,  limited. 

(d)  Press  dispatches. 

(e)  Other  dispatches. 

VI.  In  the  case  of  the  Nantucket  Shoal  light-ship,  it  will,  immediately  on 
receiving  the  vessel's  call,  acknowledge,  and   (after  receiving  vessel's  name, 
distance,  weather  report,  and  number  of  words  she  wishes  to  send)  transmit 
the  first  three  to  Newport,  and  then  tell  the  vessel  to  go  ahead  with  her 
messages. 

VII.  After  receiving  these  and  sending  the  vessel  any  message  on  file  for 
her,   the   light-ship   will  transmit   to   Newport   messages   received   from   the 
communicating  vessel  in  the  following  order: 

(a)   Government  business. 

(&)   Urgent  private  dispatches,  limited. 

(c)  Press  dispatches. 

(d)  Other  dispatches. 

VIII.  A  naval  wireless  telegraph  station  has  the  right  to  break  in  on  any 
message  being  sent  by  a  vessel  at  any  time,  and  the  right  of  way  may  be 
given  at  any  time  to  a  government  vessel  or  one  in  distress. 


APPENDICES.  193 

IX.  When    two    or    more    vessels    desire    to    communicate    with    a    naval 
wireless  telegraph  station  at  the  same  time,  the  one  whose  call  is  first  re- 
ceived will  have  right  of  way,  and  the  others  will  be  told  to  wait  and  will 
be  taken  up  in  turn.    Vessels  having  been  told  to  wait  must  cease  calling. 

X.  In   case   communication   is   not   established   with   any   ship   for   which 
messages   are   on  file,   the  naval  wireless  telegraph   station  will  notify  the 
telegraph  company  from  which  the  messages  were  received,  giving  sufficient 
information  for  them  to  identify  the  telegrams  and  notify  the  sender. 

XL  In  order  to  obtain  the  best  results,  both  sending  and  receiving  appara- 
tus should  be  tuned  to  wave  length  of  425  meters.  (Subject  to  change.) 

XII.  In  order  that  all  messages  received  at  naval  wireless  telegraph  sta- 
tions may  be  forwarded  to  ships  for  which  they  are  intended,  and  in  order 
that  all  ships  equipped  with  wireless  telegraph  apparatus  may  receive  storm 
warnings,  they  should  always  report  when  in  signaling  distance  of  a  naval 
wireless  telegraph  station. 

XIII.  The  service  being  without  charge  at  present,  the  Government  accepts 
no  responsibility  for  the  reception  or  transmission  of  messages  from  or  for 
passing  vessels.     Every  effort  will  be  made  to  transmit  all  messages  without 
error  and  as  expeditiously  as  possible.     It  must  be  remembered  that  errors 
are  not  uncommon  in  ordinary  telegraph  and  cable  messages,  so  that  due 
allowance  should  be  made. 

XIV.  In  order  that  the  service  may  be  made  as  good  and  as  useful  as  pos- 
sible,  complaints  should  be  promptly  reported  to  the  Navy  Department  as 
soon  as  possible  after  the  cause  therefor,  giving  date,  hour  and  other  details, 
to  enable  the  Department  to  investigate  the  case. 

XV.  Information   regarding  the  naval  wireless  telegraph  service   will  be 
published  in  "  Notices  to  Mariners,"  issued  by  the  Hydrographic  Office  of  the 
Navy  Department. 

(Rules  XV  to  XXXII,  adopted  by  the  International  Wireless  Telegraph  Con- 
ference of  Berlin,  1906,  are  in  force  at  U.  S.  Naval  coastwise  wireless  tele- 
graph stations.  See  Appendix  C  for  the  most  important  of  these.) 

APPENDIX  C. 

SERVICE   REGULATIONS   ANNEXED   TO    THE   INTERNATIONAL 
WIRELESS  TELEGRAPH  CONVENTION. 

[Extracts  from  International  Wireless  Telegraph  Convention,  Berlin, 
November,  1906.] 

ARTICLE  2. 

By  "  coastal  stations  "  is  to  be  understood  every  wireless  telegraph  station 
established  on  shore  or  on  board  a  permanently  moored  vessel  used  for  the 
exchange  of  correspondence  with  ships  at  sea. 

Every  wireless  telegraph  station  established  on  board  any  vessel  not  per- 
manently moored  is  called  a  "  station  on  shipboard." 

ARTICLE,  3. 

The  coastal  stations  and  the  stations  on  shipboard  shall  be  bound  to  ex- 
change wireless  telegrams  without  distinction  of  the  wireless  telegraph  system 
adopted  by  such  stations. 


194  APPENDICES. 

IV. 

It  is  understood  that,  in  order  not  to  impede  scientific  progress,  the  pro- 
visions of  article  3  of  the  convention  shall  not  prevent  the  eventual  employ- 
ment of  a  wireless  telegraph  system  incapable  of  communicating  with  other 
systems,  provided,  however,  that  such  incapacity  shall  be  due  to  the  specific 
nature  of  such  system  and  that  it  shall  not  be  the  result  of  devices  adopted 
for  the  sole  purpose  of  preventing  intercommunication. 

1.  ORGANIZATION  OF  WIRELESS  TELEGRAPH  STATIONS. 
I. 

The  choice  of  wireless  apparatus  and  devices  to  be  used  by  the  coastal 
stations  and  stations  on  shipboard  shall  be  unrestricted.  The  installation  of 
such  stations  shall,  as  far  as  possible,  keep  pace  with  scientific  and  technical 
progress. 

II. 

Two  wave  lengths,  one  of  300  meters  and  the  other  of  600  meters,  are 
authorized  for  general  public  service.  Every  coastal  station  opened  to  such 
service  shall  use  one  or  the  other  of  these  two  wave  lengths.  During  the 
whole  time  that  a  station  is  open  to  service  it  shall  be  in  condition  to  receive 
calls  according  to  its  wave  length,  and  no  other  wave  length  shall  be  used 
by  it  for  the  service  of  general  public  correspondence.  Each  government 
may,  however,  authorize  in  coastal  stations  the  employment  of  other  wave 
lengths  designed  to  insure  long-range  service  or  any  service  other  than  for 
general  public  correspondence  established  in  conformity  with  the  provisions 
of  the  convention,  provided  such  wave  lengths  do  not  exceed  600  meters  or 
that  they  do  exceed  1600  meters. 

III. 

1.  The  normal  wave  length  for  stations  on  shipboard  shall  be  300  meters. 
Every  station  on  shipboard  shall  be  installed  in  such  manner  as  to  be  able 
to   use  this   wave  length.     Other  wave   lengths   may   be  employed   by   such 
stations  provided  they  do  not  exceed  600  meters. 

2.  Vessels  of  small   tonnage  which   are  unable  to  have   plants  on  board 
insuring  a  wave  length  of  300  meters  may  be  authorized  to  use  a  shorter 
wave  length. 

IV. 

1.  The  International  Bureau  shall  be  charged  with  drawing  up  a  list  of 
wireless  telegraph  stations  of  the  class  referred  to  in  Article  1  of  the  con- 
vention. Such  list  shall  contain  for  each  station  the  following  data: 

(1)  Name,   nationality   and   geographical   location   in   the   case   of  coastal 
stations;   name,  nationality,  distinguishing  signal  of  the  International  Code 
and  name  of  ship's  home  port  in  the  case  of  stations  on  shipboard. 

(2)  Call  letters  (the  calls  shall  be  distinguishable  from  one  another  and 
each  must  be  formed  of  a  group  of  three  letters). 

(3)  Normal  range. 

(4)  Wireless  telegraph  system. 

(5)  Class  of  receiving  apparatus  (recording,  acoustic  or  other  apparatus). 

(6)  Wave   lengths   used   by  the   station    (the  normal   wave  length   to  be 
underscored). 


APPENDICES.  195 

(7)  Nature  of  service  carried  on  by  the  station. 
General  public  correspondence. 

Limited  public  correspondence   (correspondence  with  vessels  ....). 

(8)  Hours  during  which  the  station  is  open. 

(9)  Coastal  rate  or  shipboard  rate. 

2.  The  list  shall  also  contain  such  data  relating  to  wireless  telegraph 
stations  other  than  those  specified  in  Article  1  of  the  convention  as  may  be 
communicated  to  the  International  Bureau  by  the  management  of  the  Wire- 
less Telegraph  Service  ("administration")  to  which  such  stations  are 
subject. 

V. 

The  exchange  of  superfluous  signals  and  words  is  prohibited  to  stations  of 
the  class  referred  to  in  Article  1  of  the  convention.  Experiments  and  prac- 
tice will  be  permitted  in  such  stations  in  so  far  as  they  do  not  interfere  with 
the  service  of  other  stations. 

VI. 

1.  No   station    on   shipboard   shall   be   established   or   worked   by   private 
enterprise   without  authority  from  the  government  to  which  the  vessel  is 
subject.     Such  authority  shall  be  in  the  nature  of  a  license  issued  by  said 
government. 

2.  Every  station  on  shipboard  that  has  been  so  authorized  shall  comply 
with  the  following  requirements: 

(a)   The  system  employed  shall  be  a  syntonized  system. 

( & )  The  rate  of  transmission  and  reception,  under  normal  conditions,  shall 
not  be  less  than  twelve  words  a  minute,  words  to  be  counted  at  the  rate  of 
five  letters  each. 

(c)  The  power  transmitted  to  the  wireless  telegraph  apparatus  shall  not, 
under  normal  conditions,  exceed  1  kilowatt.  Power  exceeding  1  kilowatt  may 
be  employed  when  the  vessel  finds  it  necessary  to  correspond  while  more  than 
300  kilometers  distant  from  the  nearest  coastal  station,  or  when,  owing  to 
obstructions,  communication  can  be  established  only  by  means  of  an  increase 
of  power. 

3.  The  service  of  the  station  on  shipboard  shall  be  carried  on  by  a  tele- 
graph operator  holding  a  certificate  issued  by  the  government  to  which  the 
vessel  is  subject.     Such  certificate  shall  attest  the  professional  efficiency  of 
the  operator  as  regards: 

(a.)  Adjustment  of  the  apparatus. 

(&)  Transmission  and  acoustic  reception  at  the  rate  of  not  less  than  20 
words  a  minute. 

(c)  Knowledge  of  the  regulations  governing  the  exchange  of  wireless  tele- 
graph correspondence. 

4.  The  certificate  shall  furthermore  state  that  the  government  has  bound 
the  operator  to  secrecy  with  regard  to  the  correspondence. 

2.  HOURS  OF  SERVICE  OF  COASTAL  STATIONS. 
VIII. 

1.  The  service  of  coastal  stations  shall,  as  far  as  possible,  be  constant,  day 
and  night,  without  interruption. 


196  APPENDICES. 

XVI. 

Ships  in  distress  shall  use  the  following  signal: 

repeated  at  brief  intervals. 

As  soon  as  a  station  perceives  the  signal  of  distress  it  shall  cease  all  cor- 
respondence and  not  resume  it  until  after  it  has  made  sure  that  the  cor- 
respondence to  which  the  call  for  assistance  has  given  rise  is  terminated. 

In  case  the  ship  in  distress  adds  at  the  end  of  the  series  of  her  calls  the 
call  letters  of  a  particular  station  the  answer  to  the  call  shall  be  incumbent 
upon  that  station  alone.  If  the  call  for  assistance  does  not  specify  any  par- 
ticular station,  every  station  perceiving  such  call  shall  be  bound  to  answer  it. 

XVII. 

1.  The  call  letters  following  the  letters 

"  P  R  B  "  signify  that  the  vessel  or  station  making  the  call  desires  to  com- 
municate with  the  station  called  by  means  of  the  International  Signal  Code. 
The  combination  of  the  letters  "  P  R  B  "  as  a  service  signal  for  any  other 
purpose  than  that  specified  above  is  prohibited. 

2.  Wireless  telegrams   may  be  framed  with  the  aid  of  the  International 
Signal  Code. 

Those  addressed  to  a  wireless  telegraph  station  with  a  view  to  being  for* 
warded  by  it  are  not  to  be  translated  by  such  station. 

3.  METHOD  OF  CALLING  WIBELESS   STATIONS  AND  TRANSMISSION  OF  WIRELESS 

TELEGRAMS. 

XIX 

1.  As  a  general  rule,  it  shall  be  the  shipboard  station  that  calls  the  coastal 
station. 

2.  The  call  should  be  made,  as  a  general  rule,  only  when  the  distance  of 
the  vessel  from  the  coastal  station  is  less  than  75  per  cent  of  the  normal 
range  of  the  latter. 

3.  Before  proceeding  to  a  call,  the  station  on  shipboard  shall  adjust  its 
receiving   apparatus   to    its    maximum    sensibility   and   make   sure   that   the 
coastal  station  which  it  wishes  to  call  up  is  not  in  correspondence  with  any 
other  station.     If  it  finds  that  any  transmission  is  in  progress,  it  shall  wait 
for  the  first  pause. 

4.  The   shipboard   station    shall   use   for   calling  the   normal  wave   of   the 
coastal  station. 

XX. 

1.  The  call  shall  comprise  the  signal. 

the  call  letters  of  the  station  called  repeated  three  times,  the  word  "  from  " 
("  de  ")  followed  by  the  call  letters  of  the  sending  station  repeated  three 
times. 

2.  The  called  station  shall  answer  by  making  the  signal 

followed  by  the  call  letters  of  the  corresponding  station  repeated  three  times, 
the  word  "  from,"  its  own  call  letters,  and  the  signal 


APPENDICES.  197 

XXIV. 

Before  beginning  the  exchange  of  correspondence  the  coastal  station  shall 
advise  the  shipboard  station  whether  the  transmission  is  to  be  effected  in 
the  alternate  order  or  by  series  (Article  XVIII);  it  shall  then  begin  the 
transmission  or  follow  up  the  preliminaries  with  the  signal 

(invitation  to  transmit). 

XXV. 

The  transmission  of  the  wireless  telegram  shall  be  preceded  by  the  signal 

and  terminated  by  the  signal 

followed  by  the  name  of  the  sending  station. 

XXVI. 

When  a  wireless  telegram  to  be  transmitted  contains  more  than  40  words, 
the  sending  station  shall  interrupt  the  transmission  after  each  series  of 
about  20  words  by  an  interrogation  point 

and  shall  not  resume  it  until  after  it  has  obtained  from  the  receiving  station 
a  repetition  of  the  last  word  duly  received,  followed  by  an  interrogation 
point. 

In  the  case  of  transmission  by  series,  acknowledgment  of  receipt  shall  be 
made  after  each  wireless  telegram. 

XXVII. 

1.  When  the  signals  become  doubtful  every  possible  means  shall  be  re- 
sorted to  to  finish  the  transmission.  To  this  end  the  wireless  telegram  shall 
be  repeated  at  the  request  of  the  receiving  station,  but  not  to  exceed  three 
times.  If  in  spite  of  such  triple  repetition  the  signals  are  still  unreadable 
the  wireless  telegram  shall  be  canceled.  If  no  acknowledgment  of  receipt  is 
received  the  transmitting  station  shall  again  call  up  the  receiving  station. 
If  no  reply  is  made  after  three  calls  the  transmission  shall  not  be  followed 
up  any  further. 

XXVIII. 

All  stations  are  bound  to  carry  on  the  service  with  as  little  expense  of 
energy  as  may  be  necessary  to  ensure  safe  communication. 

4.  ACKNOWLEDGMENT  OF  RECEIPT  AND  CONCLUSION  OF  WORK. 
XXIX. 

1.  Receipt   shall   be   acknowledged    in   the   form   prescribed   by   the    Inter- 
national  Telegraph  Regulations,  preceded   by  the  call  letters  of  the  trans- 
mitting station  and  followed  by  those  of  the  receiving  station. 

2.  The  conclusion  of  a  correspondence  between  two  stations  shall  be  indi- 
cated by  each  station  by  means  of  the  signal 

followed  by  its  call  letters. 


198  APPENDICES. 

APPENDIX  D. 

[PUBLIC— No.  262.] 

[S.  7021.] 

An  Act  to  require  apparatus  and  operators  for  radio-communication  on 
certain  ocean  steamers. 

Be  it  enacted,  by  the  Senate  and  House  of  Representatives  of  the  United 
States  of  America  in  Congress  assembled,  That  from  and  after  the  first  day 
of  July,  nineteen  hundred  and  eleven,  it  shall  be  unlawful  for  any  ocean- 
going steamer  of  the  United  States,  or  of  any  foreign  country,  carrying 
passengers  and  carrying  fifty  or  more  persons,  including  passengers  and 
crew,  to  leave  or  attempt  to  leave  any  port  of  the  United  States  unless  such 
steamer  shall  be  equipped  with  an  efficient  apparatus  for  radio-communica- 
tion, in  good  working  order,  in  charge  of  a  person  skilled  in  the  use  of  such 
apparatus,  which  apparatus  shall  be  capable  of  transmitting  and  receiving 
messages  over  a  distance  of  at  least  one  hundred  miles,  night  or  day: 
Provided,  That  the  provisions  of  this  Act  shall  not  apply  to  steamers  plying 
only  between  ports  less  than  two  hundred  miles  apart. 

SEC.  2.  That  for  the  purpose  of  this  Act  apparatus  for  radio-communi- 
cation shall  not  be  deemed  to  be  efficient  unless  the  company  installing  it 
shall  contract  in  writing  to  exchange,  and  shall,  in  fact,  exchange,  as  far  as 
may  be  physically  practicable,  to  be  determined  by  the  master  of  the  vessel, 
messages  with  shore  or  ship  stations  using  other  systems  of  radio-communi- 
cation. 

SEC.  3.  That  the  master  or  other  person  being  in  charge  of  any  such 
vessel  which  leaves  or  attempts  to  leave  any  port  of.  the  United  States  in 
violation  of  any  of  the  provisions  of  this  Act  shall,  upon  conviction,  be  fined 
in  a  sum  not  more  than  five  thousand  dollars,  and  any  such  fine  shall  be  a 
lien  upon  such  vessel,  and  such  vessel  may  be  libeled  therefor  in  any  district 
court  of  the  United  States  within  the  jurisdiction  of  which  such  vessel  shall 
arrive  or  depart,  and  the  leaving  or  attempting  to  leave  each  and  every  port 
of  the  United  States  shall  constitute  a  separate  offense. 

SEC.  4.  That  the  Secretary  of  Commerce  and  Labor  shall  make  such 
regulations  as  may  be  necessary  to  secure  the  proper  execution  of  this  Act 
by  collectors  of  customs  and  other  officers  of  the  government. 

Approved,  June  24,  1910. 

APPENDIX  E. 

WIRELESS  TELEGRAPH  STATION  ROUTINE  FOR  UPKEEP  OF  STATION  OUTFIT. 

DAILY. 

Wipe  off  all  instruments  with  care. 
Tighten  contacts  of  receivers. 
Clean  commutators  and  collector  rings. 
Clean  zinc  oxide  from  zinc  spark  points,  if  fitted. 
Blow  water  out  of  air  lines. 
Fill  cylinder  oil  cup  and  lubricate  governor. 

In  winter,  tend  heating  apparatus  carefully  to  prevent  freezing  of  water  in 
cylinders,  pipes,  etc.,  and  keep  oil  fluid  if  necessary. 


APPENDICES.  199 

WEEKLY. 

Rub  down  slate  panels  and  instrument  cases,  examine  contacts  on  panels, 
and  vaseline  moving  contacts  lightly. 

Blow  out  armatures  and  fields  of  motor-generators,  generators,  and  motors. 

Lubricate  chains  on  engines. 

Clean  bushings  and  exterior  of  transformers  or  induction  coils. 

Wipe  off  glass  of  condenser  jars  in  air  and  clean  contacts  if  necessary. 

Clean  jar  rack. 

Pump  up  compressed  air  condensers,  if  installed. 

Clean  and  polish  inductances  and  exposed  leads  of  transmitter. 

Clean  thoroughly  and  set  up  all  contacts  of  transmitter  with  care. 

Clean  and  polish  spark  gap. 

Polish  key. 

Polish  wood,  metal,  and  rubber  of  receiver. 

Vaseline  lightly  the  contacts  of  receiver  switch  and  aerial  switch  if  fitted, 
after  cleaning. 

Clean  lightning  switch  and  vaseline  contacts  lightly. 

Clean  all  strainers. 

Lubricate  pistons  of  magnetic  air  valves  and  reducing  valves. 

Lubricate  cylinders  and  bearings. 

Lubricate  working  parts  of  valves  in  pipe  lines  and  operate  same. 

MONTHLY. 

Make  cadmium  tests  of  storage  battery,  if  installed. 

Clean  oil  injection  nozzles. 

Pack  stuffing  boxes  of  valves  in  pipe  lines. 

Clean  and  tighten  contacts  of  ground  where  accessible. 

SEMIANNUALLY. 

Change  oil  of  motor-generators,  motors,  and  generators. 

Refit  and  line  bearings  of  same. 

Empty  oil  storage  tank  and  clean  gauze  strainer. 

Dismount  and  clean  oil  tubes  of  lubricating  system. 

Dismount  and  seat  check  valves. 

Dismount  and  clean  tubes  of  feed  oil  distribution  system. 

Renew  asbestos  packing  of  oil  pump. 

Clean  port  openings,  combustion  spaces,  exhaust  ports,  joint  screws,  and 
jackets  of  cylinders,  and  renew  gaskets. 

Dismount  Leyden  jar  condenser  and  clean  thoroughly. 

Lower  aerial,  wipe  off  insulators,  oil  blocks,  overhaul  halliards,  and  renew 
same  when  necessary. 

Polish  hard  rubber  of  receiver,  etc.,  using  bisulphide  of  carbon. 


200  APPENDICES. 

APPENDIX  F. 

RESUSCITATION  FKOM  APPARENT  DEATH  FROM  ELECTRIC  SHOCK. 
BY  ATJGUSTIN  H.  GOELET,  M.  D. 

The  urgent  necessity  for  prompt  and  persistent  efforts  at  resuscitation  of 
victims  of  accidental  shocks  by  electricity  is  very  well  emphasized  by  the 
successful  results  in  the  instances  recorded.  In  order  that  the  task  may  not 
be  undertaken  in  a  half-hearted  manner,  it  must  be  appreciated  that  accidental 
shocks  seldom  result  in  absolute  death  unless  the  victim  is  left  unaided  too 
long,  or  efforts  at  resuscitation  are  stopped  too  early. 

In  the  majority  of  instances  the  shock  is  only  sufficient  to  suspend  anima- 
tion temporarily,  owing  to  the  momentary  and  imperfect  contact  of  the  con- 
ductors, and  also  on  account  of  the  resistance  of  the  body  submitted  to  the 
influence  of  the  current.  It  must  be  appreciated  also  that  the  body  under  the 
conditions  of  accidental  shocks  seldom  receives  the  full  force  of  the  current 
in  the  circuit,  but  only  a  shunt  current,  which  may  represent  a  very  insig- 
nificant part  of  the  whole. 

When  an  accident  occurs,  the  following  rules  should  be  promptly  executed 
with  care  and  deliberation: 

1.  Remove  the  body  at  once  from  the  circuit  by  breaking  contact  with  the 
conductors.     This  may  be  accomplished  by  using  a  dry  stick  of  wood,  which 
is  a  nonconductor,  to  roll  the  body  over  to  one  side,  or  to  brush  aside  a  wire, 
if  that  is  conveying  the  current.    When  a  stick  is  not  at  hand,  any  dry  piece 
of  clothing  may  be  utilized  to  protect  the  hand  in  seizing  the  body  of  the 
victim,  unless  rubber  gloves  are  convenient.     If  the  body  is  in  contact  with 
the  earth,  the  coat  tails  of  the  victim,  or  any  loose  or  detached  piece  of  cloth- 
ing may  be  seized  with  impunity  to  draw  it  away  from  the  conductor.    When 
this  has  been  accomplished  observe  rule  2.     The  object  to  be  attained  is  to 
make  the  subject  breathe,  and  if  this  can  be  accomplished  and  continued  he 
can  be  saved. 

2.  Turn  the  body  upon  the  back,  loosen  the  collar  and  clothing  about  the 
neck,  roll  up  a  coat  and  place  it  under  the  shoulders,  so  as  to  throw  the  head 
back,  and  then  make  efforts  to  establish  respiration   (in  other  words,  make 
him  breathe),  just  as  would  be  done  in  case  of  drowning.    To  accomplfsh  this, 
kneel  at  the  subject's  head,  facing  him,  and  seizing  both  arms  draw  them 
forcibly  to  their  full  length  over  the  head,  so  as  to  bring  them  almost  to- 
gether above  it,  and  hold  them  there  for  two  or  three  seconds  only.     (This  is 
to  expand  the  chest  and  favor  the  entrance  of  air  into  the  lungs.)      Then 
carry  the  arms  down  to  the  sides  and  front  of  the  chest,  firmly  compressing 
the  chest  walls,  and  expel  the  air  from  the  lungs.    Repeat  this  maneuver  at 
least  sixteen  times  per  minute.     These  efforts  should  be  continued  unremit- 
tingly for  at  least  an  hour,  or  until  natural  respiration  is  established. 

3.  At  the  same  time  that  this  is  being  done,  some  one  should  grasp  the 
tongue  of  the  subject  with  a  handkerchief  or  piece  of  cloth  to  prevent  it  slip- 
ping, and  draw  it  forcibly  out  when  the  arms  are  extended  above  the  head, 
and  allow  it  to  recede  when  the  chest  is  compressed.     This  maneuver  should 
likewise  be  repeated  at  least  sixteen  times  per  minute.    This  serves  the  double 
purpose  of  freeing  the  throat  so  as  to  permit  air  to  enter  the  lungs,  and  also, 
by  exciting  a  reflex  irritation  from  forcible  contact  of  the  under  part  of  the 
tongue  against  the  lower  teeth,  frequently  stimulates  an  involuntary  effort  at 
respiration.     To  secure  the  tongue  if  the  teeth  are  clenched,  force  the  jaws 
apart  with  a  stick,  a  piece  of  wood,  or  the  handle  of  a  pocket  knife. 


APPENDICES.  201 

4.  The  dashing  of  cold  water  into  the  face  will  sometimes  produce  a  gasp 
and  start  breathing,  which  should  then  be  continued  as  directed  above.     If 
this  is  not  successful  the  spine  may  be  rubbed  vigorously  with  a  piece  of  ice. 
Alternate  applications  of  heat  and  cold  over  the  region   of  the  heart  will 
accomplish  the  same  object  in  some  instances.    It  is  both  useless  and  unwise 
to  attempt  to  administer  stimulants  to  the  victim  in  the  usual  manner  by 
pouring  them  down  his  throat. 

While  the  above  directions  are  being  carried  out,  a  physician  should  be 
summoned,  who,  upon  his  arrival,  can  best  put  into  practice  rules  5,  6,  and  7, 
in  addition  to  the  foregoing,  should  it  be  necessary. 

FOR  THE  PHYSICIAN  SUMMONED. 

5.  Forcible  stretching  of  the  sphincter  muscle  controlling  the  lower  bowel 
excites   powerful  reflex  irritation   and   stimulates  a  gasp    (inspiration)    fre- 
quently when  other  measures  have  failed.    For  this  purpose,  the  subject  should 
be  turned  on  the  side,  the  middle  and  index  fingers  inserted  into  the  rectum, 
and  the  muscle  suddenly  and  forcibly  drawn  backward  toward  the  spine.    Or, 
if  it  is  desirable  to  continue  efforts  at  artificial  respiration  at  the  same  time, 
the  knees  should  be  drawn  up  and  the  thumb  inserted  for  the  same  purpose, 
the  subject  retaining  the  position  on  the  back. 

6.  Rhythmical  traction  of  the  tongue  is  sometimes  effectual  in  establishing 
respiration  when  other  measures  have  failed.    The  tongue  is  seized  and  drawn 
out  quickly  and  forcibly  to  the  limit,  then  it  is  permitted  to  recede.    This  is 
to  be  repeated  16  times  per  minute. 

7.  Oxygen  gas,  which  may  be  readily  obtained  at  a  drug  store  in  cities  or 
large  towns,  is  a  powerful  stimulant  to  the  heart  if  it  can  be  made  to  enter 
the  lungs.    A  cone  may  be  improvised  from  a  piece  of  stiff  paper  and  attached 
to  the  tube  leading  from  the  tank,  and  placed  over  the  mouth  and  nose  while 
the  gas  is  turned  on  during  the  efforts  at  artificial  respiration. 


INDEX. 

A  ART. 

Absorption   125,  126 

Accumulator 4 

Adjustments    197 

Aerial     113,  168-172 

Air, 

Atmospheric  pressure  of   71 

Dielectric  strength  of  151 

Amber 1,  12 

Ammeter    86 

Calibration   of    211 

Hot  wire 174,  19J9,  202,  210 

Ampere    ,. . ., 80,  93 

Definition   of 84 

International  standard   86 

Ampliphone 191 

Amplitude 55 

Decrease   of 125 

Anode 3,184 

Antenna.     (See  aerial.) 

Armature 37 

Austin 99,  100,  125,  179,  184,  206 

B 

Battery, 

Primary 3 

Solution    3 

Storage 4 

Bellini-Tosi 226 

Buzzers, 

Testing    189 

C 

Calculations, 

Basis  of  13 

Calibration 197 

Capacity 44,  92,  96 

Concentrated    75 

Distributed    75 

In  sending  sets 1"45 

Measurement  of 107,  213 

Notation  of 89 

Of  straight  wires 104 

Relation  to  self-induction  in  long  wire 59 

Specific  inductive   46 

What  it  depends  on 47 

Care  and  operation 214 

14 


'204:  INDEX. 

ART. 

Cathode     3,184 

Cell, 

Parallel 5 

Primary,  illustration  of v      3 

Secondary 4 

Series    5 

Standard    86 

Storage     4 

Centimeter     79 

Charges 1,  11 

How  created   13 

Inertia  of    53 

Signs  of 1 

Circuits, 

Closed   56,  75,  138 

Direct  connected   75 

Grounded     113 

Inductively  connected   75 

Looped 180 

Non-radiating     112 

Open .75,  168 

Oscillating 58,  60,  75,  121 

Radiating  75,  110,  112 

Stiff    182,   207 

Circular  mil 91 

Codes .216,  217 

Coherer    178,  188 

Coil, 

Coupling 174 

Loading 174 

Variometer 174 

Commutator    36 

Condenser-s     *. .     45 

Connections    of 146 

Conventional  signs  for 50 

Discharge  of 51,  52,  53,  54,  123 

Discussion  of 48,  148 

Fixed 50 

In  parallel  ,. 105 

In  series 105 

Intermittent  use  of , 124 

Kinds  of 147,  181 

Leyden  jars    50 

,   Material  of   148 

Non-oscillatory  discharge  of 94 

Oscillatory  discharge  of 51,  52 

Variable 50 

Conductors, 

Definition  of  2 

Opaque  to  electric  waves   68 

Coulomb    87,  92 


INDEX.  205 

ART. 

Counterpoise     176 

Coupling, 

Close    109 

Coefficient  of 109 

Loose    109 

Of  electric  circuits  109 

Percentage  of  110 

Perfect     109 

Current-s   3,  80,  92 

Alternating 33,  101 

Determination  of  direction  of 31 

Direct    36,   101 

Direction  of    9 

Electric 3 

Induced,  direction  of 14,  31 

Interrupted 35 

Loop   69 

Received,  measurement  of  212 

Node 69 

Production  of  by  cutting  lines  of  force  32,  33 

Pulsating    36 

Rectified     36 

Cycle     55 

Cymometers    107 

D 

Damping     55,  60 

Formula  for 117 

Measurement  of    208 

DeForest    179,    182 

Detectors    ...'..! 178 

Crystal     185 

Electrolytic 184 

Lodge-Muirhead     188 

Magnetic    187 

Primary  cell 184 

Rectifying   185 

Vacuum  tube 186 

Dielectrics 2,  46 

Rupture  of   47 

Strains  in 47 

Strength    of    149 

Table  of 150 

Direction  finders  -. 226 

Direction  senders   227 

Duddell  &  Taylor 125 

Dynamo-s 36 

Building  up  of 38 

Direct  current   39  . 

Self -exciting    36,  39 

Dyne    79 


206  INDEX. 

E  ART. 

Earth  quadrant   88 

Electric   induction 46 

Electricity  1 

Dynamic 42 

Origin  of  word *   1 

Relation  between  it  and  magnetism  16 

Source  of    31 

Frictional 1 

Static    f 1 

Voltaic 42 

Electrification, 

Duration  of    44 

Limit  of 47 

What  it  consists  of 47 

Electrode    3,184 

Electrolyte    3,  85,  184 

Electro-magnet 8 

Illustration  of 8 

Electro-magnetic  induction 12 

Illustration  of   > 15 

Methods  of  producing  current  by  31 

Electro-magnetism    8 

Electro-motive  force  3,  29,  37,  80,  84,  92 

Electrons   66 

Electroscope  1,  12,  45 

Element, 

Conventional  sign  for 5 

Negative    3 

Positive    3 

Energy, 

Forms  of 78 

Laws  of „  .     78 

Non-returnable  128 

Returnable    128 

Storage  of  , 45 

Transfer   of 159 

Erg    79 

Ether    18 

Compression  of 18 

Movements  of  20,  43 

Strain    of 18 

Stretch  of   18 

Ether  waves  64 

Absorption  of 68,  71,  125,  126 

Attenuation    of    71 

Detection  of 71,  127 

Diffraction  of 68,  73 

Earthed 113,   114 

Formation  of   66 

Free 113 

Guided    .  71 


INDEX.  207 

Ether  waves — continued.  AKT. 

Interference  of 73 

Lengths  of   64,  67,  165 

Measurement  of   199-210 

Method  of  changing  period  106 

Production    of    74 

Radiation  of  112,  113 

Reflection  of   68,  71 

Refraction  of    68,  72 

Velocity  of 66 

Exciter  39 

F 

Farad  87,  93 

Fessenden 99,  100,  178,  223 

Interference  preventer    179 

Field-s, 

Analogy  between 49 

Electric  17,  18 

Electro-static 113 

Magnetic  17,18 

Magnetic,  strength  of 84 

Fleming   99 

Foot-pound 78 

Force, 

Definition  of 78 

Field  of  7 

Magnetising    47 

Magneto-motive    , 47 

Frequency 59 

G 

Galvanometer  35,  44,  199 

Generator-s  41 

Frequency  of   130 

Sending,  description  of 129 

Gram  79 

Gravity, 

Force  of  79 

Ground  175,  176 

Connection  and  lead   175 

H 
Heat, 

Definition  of  - 67 

Velocity  of    19 

Henry 88,  93 

Hertz    65 

Hertzian  waves   65 

(See  also  ether  waves.) 


208  INDEX. 


ART. 

Horse-power    93 

Hysteresis, 

Dielectric 108 

Magnetic    .108 


Impedance   30,  101 

Inductance-s    61 

Fixed 62 

Forms  of 108,  138,  173,  174,  182 

Measurement  of 107,  213 

Variable    62 

Induction, 

Coil 27 

Electric    46 

Electro-magnetic    12,   14 

Magnetic    -. 47 

Mutual 15,  109 

Self 30,   95 

Total 57 

Inertia, 

Electro-magnetic    54 

Installation 193 

Insulators    2 

Transparent  to  electric  waves  68 

J 

Joule, 

Definition   of    84 

K 

Keys, 

Break 137 

Sending,   types   of 137 

.L 

Length, 

Electrical 30,  59 

Leyden  jar. 

(See  condensers.) 

Light, 

Definition   of    '. 19 

Velocity  of    19 

Lines, 

Of  force,  movement  of  14,  28 

Of  force,  negative  direction  of  7,  9 

Of  force,  positive  direction  of 7,  9 

Of  force,  used  as  basis  for  electric  measurements  7 

Loading    coils    179 

Loops 68 


INDEX.  209 

M  ART. 

Magnetic   induction    14 

(See  also  induction,  magnetic.) 

Magnetism     6 

Magnetization, 

Limit  of 47 

What  it  consists  of 47 

Marconi 158,  178,  227 

Martin    158 

Measurement, 

Of  coupling.    (See  wave  meters.) 

Of   damping 208 

Of  inductance  and  capacity  213 

Of  received  currents 212 

Of  sending  currents.     (See  ammeter,  hot  wire.) 

Of  wave  lengths 199  to  205 

Megohm 91 

Mercury  turbine  interrupter  129 

Microfarad 89,91,93 

Micron    ^ 91 

Microsecond    91 

Mil 91 

Milliampere 91 

Millihenry 88,   91,   93 

Millivolt     91 

Motor    41 

Motor  generator    41 


N 

Nonconductors    2,   45 

Nodes    .  68 


O 

Octave     129 

Ohm   80,  93 

Definition    of    84 

International  standard  of 86 

Legal 86 

Ohm's  law, 

Deduction  of    82 

Ondameter     107 

Operating    room    193 

Oscillating  circuit. 

(See  circuit,  oscillating.) 

Oscillation-s, 

Damped 116 

Decrement  of 117 

Definition   of    55 

Undamped 118,  218  to  225 

Oscillator     ,                                                                                                                .  112 


210  INDEX. 

P  ART. 

Permeability, 

Electric,  of  air    46 

Magnetic,  of  air,  of  iron 25 

Of  insulators    ,  46 

Pierce 104,  121,  178,  181 

Pitch     129 

Poles     3 

Magnetic    6 

North  and  south    6 

Positive  and  negative  3 

Portable  wireless 228 

Potential    87 

Effect  on  work,  period  and  amplitude  58 

Illustration  of 1,  3,  44 

Loop   69 

Node    69 

Potentiometer    v 178 

Power 78,  92,  98 

Electric,  basis  of    .' 21 

Equation   of    83 

Protective   devices    .  195 


Quenched  spark. 

(See  spark,  quenched.) 

R 

Reactance   30,  101 

Reactance  regulator   101,  135 

Receiving  apparatus   100,  177,  225 

Receiving   circuits    178 

Coupling  of '. .  : •. .  .  180 

Relay  137,  191 

Resistance    80,  92 

Illustration  of   29 

Inductive     61 

Non-inductive  61 

Radiation 115 

Standard 86 

Resonance 63,  107,  198 

S 

Saturation, 

Of  iron 38,  47 

Self-induction 30,  92 

(See  also  induction,  self.) 

Notation  of  88 

Of  straight  wires   104 

Sending  apparatus   129 

Direct    connected    139 

Efficiency  of 99 

Frequency  of    ,'. 130 


INDEX. 

Sending  apparatus — continued.  .  ART. 

Inductively  connected   140 

Regulation   of    136 

Sending  circuits, 

Types  of    138 

Sending  helix    108 

Shoemaker   179,  184 

Skin   effect    ." 103 

Solenoid, 

Core   of    25 

Illustration  of   8 

Solution, 

Battery     3 

Spark, 

Quenched   157 

Spark  gap   54,  60,  74,  121 

Cooling  of  132 

Function  of    153 

Resistance  of   153 

Rotating 134,  155 

Safety    135,  195 

Types  of   152 

Specific  inductive  capacity    46 

Table  of 150 

Standard  jar 93 

Capacity  of 94 

Static  discharges   184,  230 

Stone 137,  178,  181 

Switch, 

Lightning    : 174 

Multiple     196 

T 

Telefunken   141,  182 

Telegrams, 

Work  done  in  sending 124 

Telegraphy, 

Wireless,  fundamental  principle  of  76 

Telephones  131,  190 

Time  constant   102 

Transformer-s   74,  135 

Air   core    27 

Auto    27 

Closed  core  27 

Illustration  of   '. 27 

Open  core    27 

Oscillation     75 

Primary  winding  27,  135 

Rotary 41 

Secondary  winding  27,  135 

Stationary     41 

Step   down    27 


212  INDEX. 

Transformer-s — continued.  ART. 

Step  up    . . . 21 

Voltage  of  135 

Tuners, 

Pancake   , 182 

Tuning • 75,  140,  182,  197 

Tuning  forks 129 

U 
Units, 

Absolute 80 

'Arbitrary 79 

Electro-magnetic    ." 80 

Electro-static    89 

Fundamental    78 

Practical 80 

Theoretical    84 

V 

Variometer 141,  182 

Vibrations, 

Electrical  • 56 

Mechanical '. 56 

Volt 80,   93 

Definition   of    84 

Standard 86 

Volt  meter 86 

W 

Watt    93 

Definition   of 84 

Wave  lengths, 

Standard    " V. .   216 

Limitations  of 165 

Wave  meters 107,  199-210 

Pierce 203 

Donitz    205 

Waves. 

(See  ether  waves.) 

Wave  trains  119,  120,  121,  163 

Decrement  of  164 

Length  of    164 

Whorls, 

Electric    113 

Wien 157 

Wire,  rat  tail  174 

Wireless  telegraphy, 

Definition    of    75 

Equations 98 

Fundamental   equation  of 94 

Fundamental  principle  of   76 

Wireless  telephony 218,  219,  220 

Work 46,  78,  95,  96,  100,  124 


